ISSN 0704-3716

Sciences 11, Canadian Translation of Fisheries and Aquatic No. 4999

Studies on Dibothriocephalus latus with special reference to its life history in Japan

S. Eguchi

Original title: Kosetsu retto jochu ni kansuru kenkyu, koto ni nippon ni okeru hon jochu no hatsuikushi ni tsuite

In: Byorigaku Kiyo 3(1): 1-66, 1926

Original language: Japanese

Available from: Canada Institute for Scientific and Technical Information National Research Council Ottawa, Ontario, Canada KlA 0S2

1983

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AUTHOR - AUTEUR Sueo EGUCHI

TITLE IN ENGLISH - TITRE ANGLAIS

Studies on Dibothriocephalus latus With Special Reference to Its Life History in Japan

TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS) TITRE EN LANGUE ÉTRANGÉRE (TRANSCRIRE EN CARACTLRES ROMAINS) Kosetsu retto jochu ni kansuru kenkyu, koto ni nippon ni okeru hon jochu no hatsuikushi ni tsuite

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Byorigaku Kiyo glii■REFERENCE IN ENGLISH - RÉFÉRENCE EN . ANGLAIS Bulletin of Pathology, Nagoya

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STUDIES ON DIBOTHRIOCEPHALUS LATUS WITH SPECIAL REFERENCE TO ITS LIFE HISTORY IN JAPAN Sueo EGUCHI, Bachelor of Medicine (Aichi) (Intern, Department of Pathology, Aichi Medical College) Table of Contents Introduction Part I. The Distribution of D. latus and Some Statistical Observations Concerning This Tapeworm Chapter 1. The Distribution and Incidence of D. latus [Infection] in Europe and America Chapter 2. The Distribution of D. latus in Japan Chapter 3. Statistical Observations Concerning the Victims of D. latus Infection in Gifu Prefecture Section 1. Classification by Year Section 2. The Geographical Distribution of Victims of D. latus Infection in Gifu Prefecture and Its Relationship to the Distribution of Fish Section 3. Classification by Age Section 4. Classifications by Sex and by Occupation Section 5. Results of Examinations of Stools From Students in the Takayama Area of Gifu Prefecture Chapter 4. Summary of Part I Part II. Studies on the Second Intermediate Hosts of D. latus and Its Plerocercoids Chapter 1. The Literature on the Second Intermediate Hosts of D. latus _Section 1. History of the Discovery of Second Intermediate Hosts for D. latus and the Second Intermediate Hosts That Have Been Discovered Abroad Section 2. The Second Intermediate Hosts That Have Been Discoyered • [for D. latus] in Japan

SEC 5-25 (Rev. 81/11) ■ OZ• V TRADUCiv..h• " • „ Canard Page 2

Chapter 2. Other Observations on the Second Intermediate Hosts [of D. latus] Section 1. Investigation of Fishes From the Jintsu-gawa (A) Investigation of Masou Salmon (B) Investigation of Fishes Other Than Masou Salmon Section 2. Investigation of Fishes From the Shirakawa River, With Special Reference to Masou Salmon Section 3. Investigation of Fishes From the Kiso-gawa, With Special Reference to Masou Salmon Section 4. Investigations of Salmons From Hokkaido and the Tone-gawa Section 5. Summary of Chapter 2 Chapter 3. Morphological Observations on Plerocercoids Section 1. The Morphology of Plerocercoids Section 2. The Site of Plerocercoids' Parasitization of Masou Salmon Section 3. The State of Parasitization of Plerocercoids Within the Body of the Second Intermediate Host Postscript. Tissue Changes That Take Place in the Host As a Result of Parasitization by Plerocercoids Chapter 4. Biological Observations Concerning [D. latus] Plerocercoids, Particularly the Resistance Exhibited by Them Part III. The Growth of D. latus Plerocercoids in the Definitive Host Chapter 1. Literature on the Definitive Hosts of D. latus Chapter 2. Experimental Ingestion of Plerocercoids Obtained From Masou Salmon Caught in the Jintsu-gawa Section 1. Experimental Materials and Test Animals Section 2. Results of Ekperiments in 1922 Section 3. Results of Experiments in 1923 Section 4. Results of Experiments in 1924 Section 5. Results of Experiments in 1925 Section 6. Summary of Experiments Chapter 3. Growth of D. latus Tapeworms and Their Life-span Within the Body of Their Definitive Host 111› Chapter 4. The Author's Observation of Cases of Animals That Hire -Been Naturally Parasitized by D. latus Page 3 Chapter 5. Summary of Part III (With Special Reference to the Definitive Hosts of D. latus) Part IV. Experimental Studies on the First Intermediate Hosts of D. latus Chapter 1. History of. Research on Whether There Is a First Intermediate Host of D. latus Chapter 2. Cultivation and Growth of [D. lotus] Eggs Chapter 3. Experiments To Determine Whether [D. latus] Has a First Intermediate Host, With Special Emphasis on the Growth of the Procercoid Within the Body of the First Intermediate Host Section 1. Experimental Materials and Methods Section 2. Experiments on the Ingestion of Six-hooked Larvae by Fish Section 3. Experiments on the Interrelationships Between Aquatic Animals (Other Than Cyclops) and Six-hooked Larvae [of D. lotus] Section 4. Cyclops in Japan Section 5. Experiments on the Interrelationship Between Cyclops and Six-hooked Larvae [of D. lotus] Chapter 4. Experiments on the Migration of D. latus Larvae From Their First to Their Second Intermediate Host Section 1. Experimental Materials and Methods Section 2. Experimental Results Section 3. Summary of Experiments Chapter 5. Summary of Part IV (With Special Reference to the Life History of D. latus in Japan) Overall Summary References Explanations of Plates

O • Page 4 Introduction

Research on parasitology began in the middle of the 18th century, with the foundations of this field being laid in the 18th and 19th centuries by such workers as M iller, Bremser, Baras, and Rudolphi. In the middle of the 19th century a

number of parasites were discovered one after the other. By this time, too the first studies on the life histories of parasites had begun to appear, and the general outlines of the life histories of flukes (Trematoda) and tapeworms (Cestoda) in particular had been worked out. Moreover, from the end of the 19th century to the present the field of parasitology underwent further development as some of the hazier problems were cleared up by new studies that were carried out by several researchers. As a result, it can now be said that the field of parasitology has gradually developed to the point where [the major issues] are

about to be clarified. /P. 3 Research on tapeworms that was undertaken by Küchenmeister, Leuckart, etc.,

around 1850 yielded new information about the relationships between adult tapeworms and bladder worms (metacercoids) or cysticercoids, while even more detailed studies were published by van Beneden and Siebold, among others. In 1883 Braun discovered Dibothriocephalus latus plerocercoids in the northern pike Esox lucius, thus decisively rebutting the objections that had been frequently

raised by Knoch, Küchenmeister and others with respect to the infection route of this parasite. Since that discovery more than 10 different fish species have been identified (by Grassi, Parona, Beneden, Zschokke, Sievers, Lemeberg, Babes,

Ciurca*, etc.) as intermediate hosts of D. latus. At this time, too, a number

of questions concerning the existence of a first intermediate host for D. latus O remained unresolved, being debated over and over with no solution in sight-.- - While

*Translator's note: Inference; the text says "Ciurca Joan". Page 5 being fully aware of his poor aptitude for this task, the present author has been intrepid enough to attempt to determine the first intermediate host of D. latus and to engage in research aimed at elucidating the life history of this parasite. Meanwhile, Janicki and Rosen have been studying this topic for many years now in Switzerland, and the results of their research, published in 1919, indicated their view that Cyclops sternuus and Diaptomus gracilis are the first intermediate hosts of D. latus. This study has shed much light on the life history of this tapeworm. In spite of the fact that D. latus has extended its range into Japan, one cannot help but feel totally alone in studying this parasite in this country. The only other Japanese publication on this subject is an 1886 paper by Dr. Ijima that confirmed that Oncorhynchus perryi salmon from the Tone-gawa had been parasitized by larval tapeworms, that is, by plerocercoids. Now, since the fish

species that serve as second intermediate hosts for D. latus in Europe and the United States - i.e., species such as Esox lucius and the burbot Lota vulgaris - are completely absent from Japan, it follows that the secondary intermediate hosts used by this parasite are utterly different here than in these other regions. Consequently, it has to be stated that the life history of D. latus in Japan has yet to be clarified, and this is especially true of the stage of its history that pertains to the first intermediate hosts of this tapeworm. Investigating the issue from a different angle, [Janicki and Rosen] carried out experiments using juvenile Esox lucius and Cyclops copepods that they had obtained from nature, these species having been selected on the basis of the results of their research

on the first intermediate hosts of D. latus. Larval tapeworms that had been

allowed to develop as endoparasites in Cyclops were experimentally fed to Esox

lucius, and then the penetration of these tapeworms into the stomach wall of the fish was observed. These observations were considered to give direct evidence Page 6 that this fish was a first intermediate host of D. latus. However, this cannot be regarded as a very good approach to studying the problem. That is, the present writer regretfully believes that the research results reported by [Janicki and

Rosen] are marred by a couple of facts. To begin with, the Cyclops crustaceans and Esox lucius fish that they used in their experiments had been collected from their natural habitats; inotherwords, their study did not make use of artificially hatched specimens. As a result of this, it must be considered ad open question whether the materials used in their tests were free from infections with larval parasites that had arisen previously in nature. Another flaw in their study is that they did not seek [to discover] the entire growth cycle that the larval tapeworms undergo in the bodies of Esox lucius, and that the conclusions drawn from the experiments were not confirmed by allowing the plerocercoids that had been obtained from the parasitized Esox lucius specimens to fully develop into

adults - that is, the growth cycle of the tapeworms was not allowed to run its

full course. /p.4 In this connection it can be noted that when Dr. Muto conducted his research on liver flukes, the experiments were apparently conducted under the assumption that it could not be stated with assurance that an intermediate host had been

identified unless specimens that had not been naturally parasitized by larvae could be parasitized by artificial means. In this research chub that had been artificially hatched and reared were employed as second intermediate hosts; these fish, that is, had not been naturally parasitized by larvae. This researcher employed mud snails in the role of the first intermediate host, causing the chub to be experimentally infected by allowing cercariae to migrate into the bodies of the snails. At the outset of this study it had been confirmed that the mud snail is a first intermediate host of liver flukes. If it may be so remarked, Page 7 the research by Dr. Muto, like the research by Janicki and Rosen that was mentioned above, makes up only one phase of the process of determining the first intermediate hosts of D. latus. Be this as it may, it can be stated that these workers have made a great contribution by reaching the points they have in the investigation of the first intermediate hosts of D. latus, as [the identity of] these hosts has been a major snag in our efforts to understand the life history of this tapeworm. Without being long-winded here, suffice it to say that these are significant achievements that should not be neglected in the history of parasitology. Nevertheless, the present author has ventured to resume the research conducted here in Japan on the life history of this tapeworm, spurred on by consideration of the various points raised above. The author's investigation commenced in April, 1919; the results that were obtained through 1925 in this study on D. latus will be discussed in this paper. The author will be more than pleased if any part of this research can supplement our knowledge of the life history of D. latus.

Part I. The Distribution of D. latus and Some Statistical Observations Concerning This Tapeworm

Chapter 1. The Distribution and Incidence of D. latus [Infection] in Europe and America

If we examine how D. latus is distributed in Europe and compare the distri- butions of hooked and non-hooked types of tapeworms, we find that, although this species is not widespread and in fact occurs rarely, it can ordinarily be found in a few isolated areas as a human parasite. Moreover, serious infestations of

D. latus are believed to have been occurring since ancient times in infected areas in Switzerland and Russia, as well as in coastal areas along the Baltic Page 8 Sea. The first instance of D. latus infection reported in the literature was actually from Switzerland, with the tapeworm being most prevalent in the central and western parts of this country but also appearing in other areas on a more scattered basis. Zaeslein (1881) recorded [D. latus] infection rates in the neighborhood of 10-20% in some coastal regions -- i.e., in the Bielersee, Murteusee, Neuenburgersee, Usee and Genfersee areas. Odier, meanwhile, found that, although one-quarter of the residents in the Zenfu* area were infected with this tapeworm, the number of victims of this parasite decreased gradually with time, so that by now cases of D. latus infection are extremely rare. And Zschokke, too, reported a steady decline in D. latus parasitism in a population where the infection rate had been 10% but had dropped to no more than /p. 5 1%. According to Huss (1854), most of the people, old and young, in Norbotten** are infected with tapeworms, and yet those [children that are still] taking their

mother's milk show absolutely no evidence of them. D. latus parasitism in other areas of Turkey has also been reported. Numerous instances of parasitization by D. latus have also been reported in Russia in coastal areas along the Baltic Sea, with the earliest recorded cases going back many years. The problem has been especially noticeable in the Doprat

region, where Szydlowski (1879) conducted a study and found that D. latus eggs were contained in the stools of 10% of the students he examined. Cruse, further- more, reported that this tapeworm appeared in 6% of all corpses autopsied in this region. As discussed above, D. latus infection was originally concentrated in

Switzerland and in coastal areas along the Baltic Sea. This tapeworm, however,

• 1,

*Translator's note: Japanese romanization of unidentified place name. **Translator's note: Inference; literally, "northern Hotten". Page 9 eventually spread to neighboring regions, extending from Switzerland to southern

France, northern Italy and southern Germany. Although there had never previously been any evidence of this parasite in southern Germany, it began to be encountered in Hanburg, Holstein and Munchen, and not uncommonly, either. Bollinger (1885), moreover, reported cases of D. latus infection in other areas of Germany. As for France, Blanchard has indicated that many people in 18th century Paris may very well have been victims of D. latus infection, and yet this tapeworm is only rarely found there now. D. latus has spread to areas around the Baltic Sea, such Norway, Finland and Sweden. Infestations of this tapeworm are reported to be fairly serious in eastern and central Finland, while the incidence of D. latus infection is especially high in southern and eastern Sweden, where it occurs on an even more widespread basis than in Russia. This tapeworm has also spread further toward the south, reaching Poland and Rumania. Several researchers have published data

on the frequency of D. latus infection in these areas. According to Baranowsky, stool examinations indicated that 8.9% of the residents of Moscow are victims of D. latus infection. Kessler found that stool samples from 7.8% of the people tested in Norway were positive for this tapeworm, while bodies of this parasite could be detected in 1.17% of corpses on necropsy. Sievers (1906) went so far as to say that, in Finland, the rate of infection with D. latus was higher than the rate of infection with round intestinal worms and threadworms. Klimenko reported that 26.8% of the people he examined tested positive for parasites, and yet it is very doubtful that such infections are found as commonly now as has been mentioned by these researchers. Leon studied the frequency of infection

in Rumania and encountered 73 cases over a nine-month period. Runebergi-manwhile, found a 13% infection rate in Herujinguhorusu*, while Schaumann reported a rate

*Translator's note: Japanese romanization of unidentified place name. - Page 10

of 18.3%. Furthermore, Alessandrini (1906) has noted that [this tapeworm] has reached Alessandrini*. Krabbe (1895) conducted a study in which he classified some 400 tapeworms found among samples of parasites taken from people in Denmark. The results that he reported for this survey are shown in Table 1. • Unfortunately, most of the statistics for the frequency of occurrence of this tapeworm in the various regions cited above are relatively old. One can find almost no recent statistics on this subject in the literature. /p. 6 Therefore, it is not really clear just what the present situation is as regards the distribution and incidence of D. latus [infection]. As for regions outside of Europe, Verrill has also encountered this tapeworm on occasion in North America. Boswell and Nickerson (1906) reported three cases [of D. latus infection] from Minnesota in the United States, while two other researchers, Lake and Ngani, attracted widespread attention with their reports of finding this parasite in Madagascar.

Chapter 2. The Distribution of D. latus in Japan

Although the circumstances concerning the presence of D. latus in Japan is not known in detail for all periods of our country's history, this tapeworm is known to have occurred here since fairly ancient times. For example, according to a report by Dr. Fujikawa, this parasite has appeared in Japan for many, many years but has been described by different names, such as shiromushi ("baichong" to the Chinese), sunbyaku (or "cunbai"), etc. "Shiromushi disease" was already known by the Heian period, as it is mentioned in the oldest medical text in

Japanese history, the Ishinho, written by Yasuyori TANBA. The main source relied gl› upon by this author, the [Chinese] text Bingyuan Hou Lun by CHAO Yuanfarie -Contains

**Translator's note: Sic. Is this a misprint? Should be Allesandria? Page 11 the statement, "Cunbai are one cun [= about one inch] long, white in color and very narrow; sometimes they are also called 'Fanbaijiu'. [People become infected with them] when they eat raw grains or meat that has been grilled using skewers that contain the bark of the mulberry tree". Also in this work is the remark, "Health problems can be avoided if curdled milk is drunk immediately after eating raw fish." And there is a warning that "Growth of this worm to a length of one chi [= 1/3 meter] will have fatal consequences for the infected person." The "baichong" referred to in China do not appear to have been tapeworms of the sort that have four suckers. It is also probably safe to say that Dibothriocephalus latus would not [be a problem] here in Japan if it were not for the preference that Japanese people have for eating raw fish, a custom they have long enjoyed, and the fact that they also eat beef, pork and other meats on a frequent basis, too. On the other hand, the mere fact that the book by Yasuyori TANBA was based on a Chinese medical text does not enable us to conclude that his comments were specifically referring to D. latus. It is regrettable that there is still a dearth of reliable survey results on the distribution of D. latus [infection] in Japan. A few books contain scattered references to there being a large number of tapeworm victims in areas along the Sea of Japan, particularly in the Hokuriku districts, and it is believed that many people in the Karafuto area may be parasitized as a result of their dietary habits. Nevertheless, it goes without saying that these opinions are not based on the results of thoroughly conducted research, so that studies by many researchers will be required in the future. Although it appears that this tapeworm has spread throughout Japan, there are absolutely no detailed eatistics on the frequency of its occurrence. Several practicing physicians recently gave the author the opportunity to meet patients considered to be infected with O Page 12

tapeworms. Careful investigation revealed that D. latus could be found in these patients only on a rather rare basis; most of the cases involved infection by

hookless types of tapeworms. This finding is probably related to the fact that beef has become widely popular with Japanese in recent years, and the beef that

has been supplied from China and Korea contains relatively large numbers /p. 7

of hookless tapeworm larvae. The author has collected here the results of parasite tests that have been reported in Japan and the results of examinations for parasite eggs that have been carried out on people by various prefectural departments of health. A general perusal of these data indicated that the researchers seldom established a category for D. latus, and that eggs of this tapeworm were not observed very often at all. However, the author is unable to judge at this point

whether the seeming rareness of D. latus infection is an actual fact or merely reflects a lack of attention to this tapeworm's eggs in the investigations

concerned.

Chapter 3. Statistical Observations Concerning the Victims of D. latus Infection in Gifu Prefecture

To begin with the author would like to state that anyone who is conducting

research on D. latus should not overlook information pertaining to how the people who have been infected by this parasite are distributed. Thus, bearing in mind the need to learn more about the distribution of D. latus victims in various regions, an attempt was made to gather some statistical data on those who have been parasitized by this tapeworm in Gifu Prefecture, which is considered to be

an area where D. latus occurs rather widely among the general populace. With 411 the kind assistance of Mr. Yoshio TAKAGI, head of the Gifu Prefectural Department of Health, an initial statistical study was conducted in this area over the

three-year period 1915-1917, and a follow-up study was carried out in 1923. • Page 13 The Gifu Prefectural Medical Association collected these statistics while conducting their local health surveys, with the data subsequently being compiled from the records of persons who had been diagnosed in each given year as having had a tapeworm infection. In addition, however, it was necessary to try to get

information on people who may have been dewormed, so as to ensure that the statistics would be as complete as possible. The author has prepared tables that break down these statistical data according to five different categories. These categories are, one, the year in which the parasitism was recorded; two, the relationship between the geographical distribution of D. latus infection and the distributions of various types of fish within Gifu Prefecture; three, the age of the victim; four, the sex of the victim; and five, the victim's occupation. The data obtained for each of these • categories will be briefly discussed below. Section 1. Classification By Year

The annual breakdown of victims of D. latus infection in Gifu Prefecture

is shown in Table 2 according to the different counties and cities in the

prefecture. As these data indicate, 119 victims were recorded for 1915, 117

for 1916, and 302 for 1917, while the figure for 1923 was 46. The reason that

so many tapeworm victims were identified in 1917 is believed to be that the health surveys conducted in that year obtained more accurate data [than in other years], as there would have been no omissions. This would likely have occurred in view of the fact that all of the members of this prefectural medical society had been notified [to be on the watch for this problem] when the plans for the local health surveys were being drawn up that year. Another reason might be that the figures

for 1915 and 1916 were not analyzed until the data for 1917 were also being 4IM examined - that is, in 1918. It thus appears that the number of victims of D. Page 14 latus infection has been somewhat underestimated for the years 1915 and 1916 because the data for those years were not collected quite as attentively as was the case in 1917. The statistics for 1923 show a substantial decline in the incidence of D. latus infection, as the number of victims recorded in that year was one-seventh the number found for 1917 and about one-half of the figures for 1915 and 1916.

Section 2. The Geographical Distribution of Victims /1D. 8 of D. latus Infection in Gifu Prefecture and Its Relationship to the Distribution of Fish The statistics on the D. latus victims found in Gifu Prefecture have been broken down by district and city within the prefecture (Table 2) and also by towns and villages (Table 3). If we examine the data for districts and cities, we find that there were 101 victims in Yoshiki District and 90 victims in Ono District; these were the areas with the greatest number of recorded cases. The areas where D. latus infection occurred next most frequently were Hashimi District, with 53 cases; Masuda District, with 49 cases; Anpachi District, 46 cases; and

Mugi District, 43. Forty-two victims were identified in Gifu City, and Inaba District had 38, Kani District 22, Ibi District 21, and Kaizu District 17. Next most frequent were Kamo and Fuwa Districts, with 11 cases each, followed by Ena

District, which had 10, Toki District with 9, Yoro District with 8, Motosu District with 6, and Yamagata District with 2. A map has been prepared for incorpo- /p. 9 ration in this paper so that the distribution of these cases within Gifu Prefecture can be more readily seen. Now one fact that is of interest here from the standpoint of comparing the distribution of D. latus victims with the geography of Gifu Prefecture is that significantly more victims of D. latus infection were found in Yoshiki and-Ono Page 15

Districts than in any other districts of Gifu Prefecture. These two districts are clearly separated from the other districts in the prefecture by a water divide; they are drainage areas for rivers, the former for rivers that empty into the

Sea of Japan, and the latter for rivers flowing into the Pacific Ocean. In Yoshiki District, the Mlyagawa River, which forms the upper course of the Jintsu-gawa, and the Takahara-gawa, which is a tributary of the latter river, flow into the Sea of Japan. Meanwhile, in Ono District, the same Miyagawa River and another tributary of the Jintsu-gawa, the Kohaga-gawa, do not pass into the Sea of Japan, nor does the Shirakawa River, which forms the upper course of the Irimizu-gawa. The other districts in Gifu Prefecture are drainage areas for three major rivers that enter into the Pacific Ocean: these are the Kiso-gawa*, the Nagara-gawa, and the Ibi-gawa. That is to say, the drainage area of the Kiso-gawa takes in Ena, Toki, Kami, Kamo, Màsuda, Mugi, Inaba, Anpachi, and Kaizu Districts, while that of the Nagara-gawa includes Gifu City and Anpachi, Yamagata, Mugi and Gujo districts. Furthermore, other districts - i.e., Kaizu, Anpachi, Fuwa, Ibi and Motosu, lie within the basin of the Ibi-gawa. As stated above, the two districts in which the greatest number of victims of D. latus infection were found were Ono and Yoshiki Districts, both of which lie in the drainage area of rivers that flow into the Sea of Japan. Few cases of parasitization by this tapeworm were noted in the districts situated within the drainage area of rivers that empty into the Pacific Ocean. Table 3 shows the figures recorded for different towns and villages in the three counties in the Hide region where the incidence of D. latus infection was found to be unusually high. Examining these data, we find that, in Ono District, the town of Takayama (54 cases) and Kyomi village (25 cases) had more victims

*Translator's note: Inference; there is an apparent misprint in the text. Page 16 than the others, while in Yoshiki District the two towns of Furukawa (15 cases) and Funatsu (9 cases) were the most affected. All of these localities lie within the drainage area of the Jintsu-gawa, and they all are considered to be either primary fishing grounds for masou salmon* or areas where fish that have spawned in the Jintsu-gawa concentrate. Furthermore, in Masuda District, the towns or villages where the highest number of D. latus victims occurred were Sakashimo (12 cases) and Hagiwara (6 cases). Although they lie within the drainage areas of the Masuda-gawa and Hida-gawa Rivers, [the latter of which] forms the upper course of the Kiso-gawa, both of these towns reportedly receive frequent supplies of fish from Takayama in Ono District, a town where fish are plentiful. Thus we can state it to be a fact that parasitization by D. latus is encountered most commonly in localities situated in the basins of rivers that flow into the Sea of Japan. An interesting and important way to discover the source of D. latus parasitism - i.e., the second intermediate host of this tapeworm - is to compare the distri- bution of victims of D. latus infection in Gifu Prefecture with the distribution of fish in that region. A map showing this relationship has been prepared and incorporated in this study. Examining this map, we see that the principal type of fish caught in Yoshiki and Ono Districts is masou salmon, with lesser amounts

*Translator's note: In Japanese, "masu". This name is commonly translated as "salmon trout", "freshwater trout", or simply "trout". The INPFC, however, stipulates that this term shall be reserved for the pink salmon Oncorhynchus gorbuscha. Nevertheless, the author of the monograph translated here evidently was using "masu" in a different sense. Although at times he seems to have intended the word to be equivalent to salmons in general, he usually indicates that he is referring specifically to the species Oncorhynchus masou, i.e., the so-called Japanese masou (or "masu") salmon, or the species Oncorhynchus perryi (he regards them as synonymous). These days the INPFC designates the masou salmon as "yamame", but this term is used by the author to designate Salmo perryi. It thus ââears that the terminology used for salmonids in the 1920s, the period in which this work was written, was significantly different in some cases from the terminology of today. Page 17 of sweet smelt* (Plecoglossus altivelis) and chum salmon being landed along with some chub (Tribolodon hakonensis), char (Salvelinus pluvius), etc. Sweet smelt

is the main type of fish caught in the Kiso-, Nagara- and Ibi-gawa, which flow into the Pacific Ocean. The fish caught next most frequently in these rivers

is grass carp; relatively little masou salmon is landed. Carp (Cyprinus carpio) and eel, meanwhile, are caught in fairly large numbers in the drainage areas of

these rivers. In addition, some rainbow trout can be found in the Ibi-gawa. As can be seen in the appended map, the areas where many victims of D. latus

infection are found are also areas that serve as the principal fishing grounds

for masou salmon. Moreover, among the localities that are situated in the drainage

areas of rivers that flow into the Pacific Ocean, those where masou salmon are fished were found to have more victims of this tapeworm than the other areas

where masou salmon are not caught.

Section 3. Classification by Age

Table 4 shows the breakdown by age of the victims of D. latus /p. 10 infection. As can be seen from this table, most of those infected with this

tapeworm were between 20- and 40-years-old, with the next most frequent age group

being those in the 40 to 50 range. Far fewer victims were found in the age ranges

15-20 and 50-60, and victims below the age of 20 or over the age of 60** occurred even more rarely. Older people probably have a low incidence of D. latus infection on account of the fact that they make up the lowest proportion of the general

population and also are careful about the foods they eat. Those in the 40-50 age range, on the other hand, would be expected to suffer more cases of tapeworm

infection in view of their dietary habits - the alcohol they drink, the foods

411› *Translator's note: Also known as gyu. **Translator's note: Inference; the text says 50. Page 18 they eat, and the more lavish variety of their diet, too, particularly the greater opportunity they have for consuming raw fish, which are a source of parasitization by D. latus. Meanwhile, no infants below the age of 1 year were found to be

infected with D. latus. This finding can probably be explained by the fact that the babies were receiving only their mother's milk and absolutely no other source of food during this period, with the result that they had no opportunity to be parasitized by the tapeworm. If we examine the problem from this viewpoint, we can say that D. latus can parasitize people of any age, and there are no great

differences between any of the age groups in this regard. Consequently, the age-related factors that make it advisable to be especially careful about being infected with hookworms or intestinal worms do not seem to apply to the case of D. latus infection. Although Huss and Wolchius reported instances where this tapeworm was detected in infants, it can still be safely stated that in Japan,

where children are weaned at a late age, there will probably be almost no cases at all where babies are found to have been parasitized by D. latus.

Section 4. Classifications by Sex and by Occupation Dibothriocephalus latus most often parasitizes males, as the number of male victims of this tapeworm was found to be approximately three times the number

of females (see Table 5). This difference in rates of infection by D. latus can probably be explained by the fact that the tapeworm is acquired by eating its second intermediate host, which may be raw or inadequately cooked /p. 11 fish, and that in Japan, males customarily eat a richer, more varied assortment of foods than females, who make do with a more spartan diet of vegetables. As

far as occupations are concerned, no notable differences have been discerned in the incidences of D. latus infection in different work groups. The tapeworm • farming or business, but no was found more often in people who were engaged in • Page 19 other significant differences were observed (Table 5). Section 5. Results of Examinations of Stools From Students in the Takayama Area of Gifu Prefecture

As could be seen from the statistical data on the victims of D. latus infection in Gifu Prefecture that were presented in the above tables, Yoshiki and Ono Districts clearly had the most cases of D. latus infection in Gifu Prefecture. The author therefore selected this region as a study area, making trips there every year for research purposes. In May, 1923, during a visit to Takayama in Ono District, the author investigated the tapeworm parasitism occurring in students, using as subjects members of two schools, the Takayama Girls' High School and the [Takayama] Girls Elementary School. With the helpful assistance of the schools' physician, Mr. Tatsuro NISHIMOTO, statistics were compiled on gl> the number of students [whose stools] were found to contain the eggs of parasites and the proportion of these latter students who were discovered to carry tapeworms. The results of this study are shown in Tables 6 and 7. Among the 277 high school girls tested, 193 (69.67%) were found to harbor parasite eggs; one of the students (0.36%) had the eggs of D. latus. As for the elementary school students, 1,233 were tested, and the eggs of parasites were discovered in 867 (69.69%) of them. Four of these children (0.32%) harbored the eggs of D. latus. In spite of the fact that this tapeworm's eggs have appeared only very rarely in stool examinations conducted on students attending schools in other prefectures, five students in the two schools in this area were found to be victims of D. latus infection. This cari be considered to be an indication that tapeworm parasitism is a real

problem in this region, so that the fact that tapeworms are prevalent there should not be ignored if the school children and other residents of the area are to ..-- - II maintain their health. /p. 12 Page 20 Chapter 4. Summary of Part I /p. 13

Dibothriocephalus latus is found in the United States and Europe, with this

tapeworm mainly being found in Switzerland and in coastal areas around the Baltic Sea. Although it is now found in many areas, D. latus occurs very rarely everywhere except these two regions. Moreover, in spite of the fact that this parasite has been fairly well established in these two regions since ancient times, it seems to be found much less frequently now than in the past. Here in Japan, D. latus is widely distributed in the Hokuriku districts and it has often been discovered in various other areas of the country, too. Contrary to what has been dbserved in Europe and in the United States, the hooked type of D. latus seems to be more common here than the hookless variety. The • author has prepared statistical tables of tapeworm victims based on the results of surveys that were carried out in 1915, 1916, 1917 and 1923. Examining the data in these tables, it would appear that tapeworm victims are very numerous in areas around the Sea of Japan, particularly in the Hokuriku districts, and in areas that serve as basins for rivers, for example, the Jintsu-gawa drainage area. On the other hand, this tapeworm is found only very rarely in the drainage

areas of rivers that empty into the Pacific Ocean. As for how the victims of D. latus infection break down by age, most of the cases detected involved people between 20- and 40-years-old. However, this finding most likely reflects the fact that people in this age group have more opportunities to eat raw fish; it is the author's belief that age per se has virtually no intrinsic significance

as far as infection by this tapeworm is concerned. The subjects of the surveys were also classified according to occupation and sex, and it appeared that the • only relevant differences were related to whether or not the person's ddify living Page 21 conditions were such as to lead to the consumption of raw fish, which are inter- mediate hosts of this tapeworm. Furthermore, if we consider the fact that most of the people who are parasitized by D. latus [acquire] the tapeworm in

May, June or July, we cari note that this period corresponds to the fishing seasons for masou salmon and egeet smelt. Moreover, coMparing the distribution of D. latus victims with the distribution of fish in Gifu Prefecture, we find that there is a distinct relationship between the two, since, as discussed in Section 2 of Chapter 1, the regions where many victims of this parasite are found are areas that serve as either the main breeding grounds of masou salmon or as areas where these fish are concentrated. Considering these facts, it is not difficult to imagine that masou salmon are very likely the primary source of parasitization by this tapeworm in Gifu Prefecture. However, it was decided that an experimental study should be carried out to ascertain whether fishes other than masou salmon

were intermediate hosts of D. latus, too, and whether masou salmon were indeed the main source of parasitization by this tapeworm. This research is discussed in detail in the subsequent parts of this monograph.

Part II. Studies on the Second Intermediate Hosts /p• 14 of D. latus and Its Plerocercoids

Chapter 1. The Literature on the Second Intermediate Hosts of D. 1atus

Section 1. History of the Discovery of the Second Intermediate Hosts of D. latus and the Second Intermediate Hosts That Have Been Discovered Abroad

Before we can discuss the second intermediate hosts of Dibothriocephalus latus, we should first give some idea of the history of the research that has been conducted on the infection route of this tapeworm. Two main approaphes • were taken in the studies that were made during the period when the infection • Page 22 route of D. latus was still unknown. One type of research consisted of exper- imental studies in which an attempt was made to cause infection using cultured eggs; in the other type of research, an attempt was made to determine the infection

route by studying intermediate hosts. From 1861 through the following year, three researchers working in Russia, Germany and France - Knoch, Leuckart and Bertolus - successively published théir own treatises on this subject. Although all three of these writers recognized that the eggs of this tapeworm hatch in

water during a warm period, and that the liberated larvae possess flagella and three pairs of hooks, they each espoused their own views with respect to the growth of this tapeworm beyond its six-hooked (hexacanth) larval stage and the path it takes when it enters the human body, and defended these views against one another. Leuckart and Bertolus believed that the six-hooked larva that emerges • as described above probably penetrates, like the Trematoda, into some intermediate host and then develops into a cysticercus or bladder worm; in their view, the intermediate host that the (larva] seeks out is in all likelihood an animal in an aquatic environment, with fishes in particular making suitable hosts. At that time these authors were frequently able to detect tapeworm larvae in the flesh and internal organs of fishes, and, on the basis of their morphology, these larvae were regarded as being those of D. latus. They likened these larvae to those that Rudolphi had described as belonging to the species Ligula nodosa. Subsequently Leuckart attempted to find experimental confirmation of these other researchers' views, having fishes referred to as "Follenbarschll consume six-hooked larvae and eggs that contained them. However, since these experiments yielded negative results, Leuckart came to the conclusion that aquatic animals other than fishes must be the intermediate hosts of D. latus. • Knoch opposed the view of Leuckart and Bertolus on this issue, stating that Page 23 the hexacanth phase of D. latus does not have much significance as far as the infection route of this tapeworm is concerned, and that it plays no more than a minor role in the dissemination of the parasite. According to Knoch, the eggs of D. latus are more important in this regard, for the eggs by themselves can produce infection. Therefore, in his opinion, there is no need at all for an intermediate host in cases of D. latus infection. Knoch's views, that is, stemmed from animal experiments that he performed, as D. latus tapeworms were detected in dogs and other mammals when they were necropsied from one week to one month after having been fed the eggs of this parasite. Nevertheless, this study had several shortcomings and has been rejected by a number of workers. Leuckart and his colleagues, moreover, repeated Knoch's experiments and obtained negative results in every instance. In 1883 Braun published a paper concerning the question of the intermediate hosts for D. latus. His work was a major advance in illuminating the infection route and life history of this parasite. Braun discovered larval tapeworms in the viscera and muscles of Esox lucius and Lota vulgaris in Dover. When these fishes were fed to animals, the animals became infected, and positive results

were also obtained when they were ingested by human beings for experimental purposes. With Braun's publication great strides were taken in advancing our knowledge of the life history of this tapeworm, and other papers on the /p. 15 intermediate hosts [of D. latus] began to appear everywhere, one after the other. In 1886 Grassi discovered larval tapeworms in Esox lucius in Sicily, and in the

same year Parona likewise discovered larval tapeworms in both Esox lucius and the perch Perca fluviatilis in various lakes (Lego Ginerva, Lago Magiorre, Lago di Decco, etc.) in northern Italy. Two other researchers, van Beneden and Edward, • also regarded Esox lucius as an intermediate host [of tapeworms]. When Fritz Page 24 and Zschokke investigated a number of different types of fish in Zenfu*, Swit- zerland, they found that Esox lucius and Coregonus fera were infected with comparatively few larval tapeworms, whereas the Lota vulgaris they examined usually contained tapeworm larvae. Moreover, the larval tapeworms that they discovered in Trutta vulgaris, Thymallus vulgaris and Trutta lacustris were believed to be the larvae of Dibothriocephalus latus. Meanwhile, Klichenmeister published a paper in which he took issue with Braun's conclusions, stating that Lachs (Salmo salar) was very likely an intermediate host [of D. latus], but both Braun and Leuckart roundly disputed this suggestion and eventually showed it to be untenable. In addition, Sievers reported that Esox lucius, Perca fluviatilis, Acernia cernua, and Coregonus albula in Finland served as intermediate hosts [for D. latus], while Loneberg discovered larvae of D. latus in Esox lucius, Coregonus laveretus and C. albula in Switzerland, and Babes reported finding one larva of this tapeworm in 15 Esox lucius from Rumania that he examined. More recently, Ciurca**, performing research in the Donau*** region in 1911, discovered that seven out of 109 Esox lucius and one out of 54 Perca [fluviatilis] she studied contained plerocercoids of D. latus. Thus quite a few second intermediate hosts have now been proposed for Dibothriocephalus latus in Europe; at present the list includes more than 10 different species.

*Translator's note: See note on p. 8 of translation. **Translator's note: See note on p. 4 of translation. ***Translator's note: Japanese romanization of unidentified place name. Page 25

Section 2. The Second Intermediate Hosts That Have Been Discovered [for D. latus] in Japan Although, as was stated in Chapter 2 of Part I of this work, D. latus has existed in Japan since ancient times, the life history of this tapeworm has remained completely obscure. However, Dr. Isao IJIMA, drawing upon the results obtained by Braun in his research on the intermediate hosts of D. latus, also believed that pikes such as Esox lucius were intermediate hosts of this tapeworm. Nevertheless, since fishes such as Esox lucius and Lota vulgaris are completely absent from Japanese waters, some other intermediate host must be found for the D. latus tapeworms occurring in this country. Here we can note that Dr. Ijima investigated Oncorhynchus perryi salmon from the Tone-gawa and discovered a type

of larval tapeworm in the fishes' flesh that was not encysted. Dr. Ijima sent • some of these larvae to Leuckart, who identified them as being identical in every respect to the plerocercoids of Dibothriocephalus latus. Furthermore, Dr. Ijima, both on his own and together with a colleague, Mr. Kikuchi, eNallowed [these] larval tapeworms, and it was found that adult tapeworms only developed /p. 16

in one of the two subjects. This research enabled an intermediate host of the D. latus tapeworms in Japan to be identified. Nevertheless, for a long time after this study no research on this parasite was carried out in Japan, with the result that there were still no published reports that investigated in detail the distribution of D. latus and the incidence of infection with it, and such

questions as to whether the aforementioned [masou salmon] is the sole intermediate host of this tapeworm in Japan remained unanswered. • • Page 26

Chapter 2. Other Observations on the Second Intermediate Hosts [of D. latus]

As was discussed in Part I, the author conducted a study in an attempt to determine the relationship between the geographical distribution of the people within Gifu Prefecture that are infected with D. latus and the distribution of fish within that prefecture. If we examine the map that was obtained as a result of the above research, we find that most cases of D. latus infection occurred within the drainage area of the Jintsu-gawa, which flows into the Sea of Japan, and that relatively few of these tapeworm victims were found in the the Kiso-gawa basin, although such cases did exist. Consequently, the author investigated the extent to which the fishes found in the Jintsu-gawa have been parasitized by D. latus plerocercoids, with particular attention being given to the question of parasitism occurring in the masou salmon. To date the author has examined the following types of fishes to determine the extent of parasitism by plerocercoids. (a) Fishes from the Jintsu-gawa (including the upper reaches of the Jintsu-gawa, i.e., the Miyagawa, and the Takahara-gawa and Kohaga-gawa, which are its tributaries): Masou salmon, chum salmon, sweet smelt, char, chub, the carp Cyprinus carpio, the trout Salmo perryi, bullhead (Cottus pollux), dace (Leuciscus

macropus), greenling (Hexagrammos otakii), loach (Misgurnus anguillicaudata); and, in addition to fish, frogs, snakes, and chickens; (h) Fishes from the Kiso-gawa (including its tributaries the Hida-gawa, the Maze-gawa, and the Masuda-gawa): _—_- Masou salmon, grass carp, char, sweet .smelt, the carp Zacco platypus, UNEDITED TRANSI_AIIOU dace, and the carp Cyprinus carpio; For only TR ADUCT ION N Infarnu,',:ert Page 27 (c)Fishes from the Nagara-gawa:

Grass carp and sweet smelt; (d)Fishes from the Shirakawa River: Masou salmon; (e)Fishes from the Tone-gawa: (f)Fishes from Hokkaido: /p. 17 Coho salmon (Oncorhynchus kisutch) and chum salmon. As stated above, the author carried out a detailed investigation on most of the fishes cited above. So far the author has been able to confirm that plerocercoids of D. latus are present in the Japanese masou salmon Oncorhynchus masou. The author will now attempt to indicate the frequency with which this type of fish has been parasitized by D. latus plerocercoids in various rivers.

Section 1. Investigation of Fishes From the Jintsu-gawa The upper course of the Jintsu-gawa is known as the Miyagawa, and the Jintsu-gawa is confluent with the tributaries the Takahara-gawa and the Kohaga-gawa. The Kohaga-gawa flows through the Ono District and the Takahara-gawa flows through the Yoshiki District of Gifu Prefecture, while the Miyagawa passes through both of these districts. These rivers join to form the Jintsu-gawa, which then flows through Toyama Prefecture and out into the Sea of Japan. (A ) Investigation of Masou Salmon When spring comes masou salmon return from the sea and swim upstream to

spawn. During April and May masou salmon are most numerous in the lower reaches of the Jintsu-gawa, but in June and July they are being caught around the boundary between Toyama and Gifu Prefectures, which occurs almost at the upper reaches of the Jintsu-gawa, or they may even appear still further upstream. By August • and September the masou salmon have ascended to locations at the uppermost part Page 28 of the river that are suitable for spawning. Since these regions are very sparsely

inhabited, and the people who do live there reside in rather isolated ravines, it is very difficult to catch the masou salmon at these areas. Not only this, but fishing of these masou salmon during their spawning season is strictly forbidden by prefectural ordinance. The author primarily studied masou salmon that had been caught in the spring, during May and June, at the lower sections of the river. In addition, however, some of the masou salmon investigated were caught in mountain streams during the spawning season, with special permission from the prefecture. Study conducted in 1922 From May 5 to June 7 of this year the author visited the town of Takayama in Gifu Prefecture to investigate masou salmon caught in the Jintsu-gawa. Of the 28 fish examined, five - that is, 17.8% - were dis- O covered to be infected with plerocercoids of D. latus. Two of these infected masou salmon were found to have one plerocercoid apiece; one of the fish had three plerocercoids; and the remaining two were each parasitized by five plero- cercoids. Study conducted in 1923 As in the previous year, the author visited Takayama in Gifu Prefecture in 1923 to investigate fish caught in the Jintsu-gawa between May 24 and June 8. These fish, which ranged from 47 to 63 am in size, were necropsied and examined for plerocercoids. Positive results were obtained

for 10 of the 23 masou salmon - i.e., for 43.6%. The number of larval tapeworms infecting each fish ranged from 1 to 15, with one larva being found in three of the fish, two larvae in three of the fish, four larvae in two of the fish, five

larvae in two of the fish, and 15 larvae in one of the fish.

Study conducted in 1924 Investigations were also carried out /p. 18 • in both the spring and fall of 1924. In the spring study, which was conducted Page 29 from May 21 to May 29 in Takgyama in Gifu Prefecture, the author examined 12 masou salmon that ranged in size from 40 to 50 cm. Three* of these fish - i.e., 25%* - were discovered to be infected with plerocercoids of D. latus; one of the specimens had been parasitized by one plerocercoid, one was parasitized by three plerocercoids, while one** of the fish harbored six plerocercoids. Furthermore,

the plerocercoids discovered in the masou salmon that had been caught in the spring were observed to be of various sizes, as they ranged from being rather immature and weak to being quite developed in size. When the masou salmon return upstream during the fall to spawn in mountain streams located in remote valley areas, they pass through the Hida and Mino regions. Since it is not legal to fish masou salmon during this period, the author had to obtain special permission from the prefecture for this study. • The author visited Kyomi village in the Ono District of Gifu Prefecture between September 29 and October 10, but was barely able to catch six masou salmon despite

repeated attempts. When these fish were examined, two - i.e., 33.3% - were found

to have been parasitized by plerocercoids of D. latus. One of the two infected fish possessed a single plerocercoid, whereas the other was parasitized by six. All of the plerocercoids found in the masou salmon in the fall study had attained a large size.

Study conducted in 1925 The author conducted another study from April

24 to June 11, 1925, in Toyama Prefecture. In this study 16 masou salmon from the Jintsu-gawa were examined. Four of these fish, which ranged in size from

45 to 65 am, were found to have been parasitized by D. latus plerocercoids; this

*Translator's note: Sic. **Translator's note: The text says two, but the information provided in • Table 8 clearly indicates that the number intended here was one. • Page 30 comes to 50% of the specimens. Between one and eight plerocercoids were detected in each of the infected masou salmon. If we combine the results from the studies carried out in the four years referred to above, we note that 28 of the 85 masou salmon investigated - i.e., 32.94% - were infected with plerocercoids of D. latus. The number of plerocercoids appearing in each fish was often not very great; as a rule between one and five of these larval tapeworms were found, although occasionally six, eight, or, rarely, as many as 15 would be present. (See Table 8.)

(B) Investigation of Fishes Other Than Masou Salmon /p. 19 The question of whether any fishes other than masou salmon serve as an

intermediate host for Dibothriocephalus latus tapeworms poses an interesting research topic. Consequently, in the studies performed from 1922 to 1925, the author investigated other salmon-like types of fish in addition to the afore- mentioned masou salmon, including chum salmon, trouts, char, and sweet smelt, etc., as well as most of the non-salmonid types of fishes [in these waters], including chub, and fish commonly referred to as dace, bullhead, and greenling. Detailed examinations were made of these other fishes, too. Plerocercoids of D. latus, however, were not detected in any of these specimens. In only one instance, in the abdominal cavity of a bullhead, was a plerocercoid-like body

detected. Close observation showed that this plerocercoid-like body was dissimilar in some respects from the plerocercoids of D. latus. When this plerocercoid-like body was experimentally fed to a dog, negative results were obtained as no adult worm eventually formed. Therefore, the experiment concluded without it being possible to establish just what sort of tapeworm this plerocercoid belonged to. From that point on the author paid special attention to the bullhead specimens, • but in each case negative results were obtained. Furthermore, since chum salmon • Page 31 resembles masou salmon more closely than any of the other fishes, chum salmon promised to be the most interesting of the other fishes studied, and accordingly special attention was also paid to it. To date the author has examined 13 chum salmon in these studies. This does not represent a very large number of specimens. However, of the 13 examined so far, none have been found to be infected with plerocercoids of D. latus. Of course, since very few chum salmon are caught in the Jintsu-gawa, it cannot be said as yet that these fish have been adequately studied. Further detailed investigation of chum salmon is required. Nevertheless, the results of the studies that have been conducted to date would seem to indicate that chum salmon is not an intermediate host of D. latus.

Section 2. Investigation of Fishes From the Shirakawa River, With Special Reference to Màsou Salmon The Shirakawa River flows through the Ono District of Gifu Prefecture and then enters Toyama [Prefecture] where it becomes the Imizu-gawa and empties into the Sea of Japan. On two occasions in April, 1925, the author conducted detailed studies of masou salmon from the Shirakawa River, examining five specimens in all. One of these five fish was discovered to have been parasitized by a single plerocercoid of D. latus. Inotherwords, we can state that 20% of the masou salmon caught in the Shirakawa River gave positive results when studied for parasitism by D. latus plerocercoids.

Section 3. Investigation of Fishes From the Kiso-gawa, /p. 20 With Special Reference to Màsou Salmon The Kiso-gawa is a major river that passes through Nagano, Gifu, Aichi, and Mie Prefectures. The Kiso-gawa is confluent with several tributaries - the Hida-gawa, Masuda-gawa, and Maze-gawa; moreover, the Nagara-gawa and Ibi-gawa • also should be regarded as tributaries of it. When the author first undertook O Page 32 his investigations on the life history of Dibothriocephalus latus, he began by studying, in 1919, fishes that had been caught in the Kiso-gawa, giving special attention to masou salmon. Most of the masou salmon that the author used in these studies came from the portions of the river that flow through the boundary between Aichi and Gifu Prefectures, and some of the masou salmon had been caught in the Maze-gawa and Hida-gawa. The masou salmon caught in the autumn were taken from mountain streams at the upper reaches of the Maze-gawa. Moreover, fishes other than masou salmon were also caught from the Kiso-gawa and Nagara-gawa. The masou salmon taken from the Kiso-gawa were quite a bit smaller than those caught in the Jintsu-gawa, so much so, in fact, that at first glance one could not help but wonder if they might not belong to a different species. The length of the specimens examined here only ranged between 20 and 40 cm. More- over, of the 25 masou salmon from this river that were studied in 1919, not one was observed to be infected with plerocercoids of D. latus; and when an additional nine masou salmon were examined in 1921, and 10 more in the spring of 1924, not even a single plerocercoid could be detected. Thus, even though a large number

of masou salmon were studied in detail in various years between 1919 and 1924, negative results were obtained in every instance. These findings have led the author to question the assumption that the masou salmon in the Kiso-gawa had to be infected with the plerocercoids of this tapeworm. Nevertheless, in view of the fact that Professor Hayashi is reported to have become infected with D. latus as a result of having eaten masou salmon given to him by someone living near the Kiso-gawa, the question of whether masou salmon in this river may carry these tapeworms must still be considered an open issue. So far we can only state that the rate of infection of masou salmon with this parasite is likely to be quite O low. At this point, the author mustered his courage for another expedition to • Page 33 the mountains and, in September, 1924, once again travelled to the upper reaches of the Maze-gawa, where, with special permission from the prefecture, and with no small effort on his part, he was able to catch three masou salmon as they fought their way upstream to spawn. When these three fish were examined closely, it was found that one them contained a single plerocercoid of D. latus, which was, moreover, very immature in development. This plerocercoid was discovered in a a dorsal layer of muscle near the fish's skin. Subsequently, in May, 1925, the author again examined six masou salmon, but obtained negative results. The findings described above seem to confirm that masou salmon in the Kiso-gawa are indeed infected with D. latus plerocercoids, but the rate of infection with these tapeworm larvae is extremely low. In the studies that have been conducted by the author to date, a total of 53 [masou salmon from this river] have been investigated, but only one - a mere 1.89% of the sample - gave positive results [for D. latus parasitism]. In 1919, 1922 and 1924, the author also made studies of fishes other than masou salmon that were taken [from the Kiso-gawa]. A number of different fishes were closely investigated, including grass carp, char, sweet smelt, the trout Salmo perryi, the carp Zacco platypus, the carp Cyprinus carpio, and dace that had been caught in the Kiso-gawa (including the Maze-gawa.and the Masuda-gawa),

and grass carp and sweet smelt from the Nagara-gawa. Nevertheless, in these studies, too, not even a single plerocercoid could be detected in these fishes, which were suspected of having been parasitized by them. /p. 21

Section 4. Investigations of Salmons From Hokkaido and the Tone -gawa Mhsou Salmon From the Tone-gawa The author was kindly given six masou salmon from the Tone-gawa by his friend, Mr. Kazushige HARA, in 1919. When these salmon were ,closely examined, the author was unable to detect the • Page 34 presence of any plerocercoids of D. latus. Dr. Ijima previously reported that he had observed larval tapeworms in masou salmon caught in the Tone-gawa; indeed, he even stated that he expected nearly all of the masou salmon [from this river] to be infected with such parasites. However, since the masou salmon that Dr. Ijima studied had been purchased from the Tokyo Municipal [Salmon and Trout Hatchery], the actual origin of at least some of his specimens could well be unknown. If the salmon in these waters have in fact been infected with these

tapeworms for centuries, it must be considered strange that the author has now been unable to observe any plerocercoids in his investigations. Or, viewed in another light, perhaps it can be said that, by pure chance, Dr. Ijima only happened to examine specimens that had been parasitized by plerocercoids, leading him to think that [virtually] all of the masou salmon there were infected. This could • explain the discrepancy. Another explanation might be that the present author only had negative results because he did not study enough samples; alternatively, it could be argued that the rate of parasitism by plerocercoids used to be high but has gradually been declining. Coho Salmon From Hokkaido Five coho salmon were also examined by

the author on July 10, 1925, in Otaru, Hokkaido. In this case, too, no D. latus plerocercoids were found. These coho salmon, however, [were not from the Otaru

area but] came from northern Hokkaido and Karafuto. /p. 22 Chum Salmon From Hokkaido In addition the author examined six chum salmon from Hokkaido that had been sent to him in a frozen state in January and February, 1924. Once again, in each instance negative results were obtained, as not a single plerocercoid of D. latus was detected. Section 5. Summary of Chapter 2 As has been mentioned above, in the years since Braun's discovery some dozen

or so papers have already been published abroad on the second intermediate hosts • Page 35 of Dibothriocephalus latus. However, none of the intermediate hosts discussed in these publications are found in Japan. Dr. Ijima has suggested that the salmon Oncorhynchus penzi. is an intermediate host of this tapeworm. The present author has been attempting to identify second intermediate hosts of D. latus since 1919. Many different species of fish have been examined in the course of this research, but only one species - the masou salmon Oncorhynchus masou Blebord - has been discovered to carry plerocercoids of this tapeworm. Furthermore, the rate of parasitism by the larvae of this tapeworm was found to be high in masou salmon that had been caught in rivers flowing into the Sea of Japan, but such infections occurred only very rarely in masou salmon fished from rivers that empty into the Pacific Ocean. That is to say, positive results for

parasitism were discovered in 28 out of 85 (32.94%) of the Oncorhynchus masou specimens that had been caught in the Jintsu-gawa, which falls into the former

category, while one out of five (20%) of the masou salmon from the Imizu-gawa - i.e., from the Shirakawa River - were infected. In contrast, positive results were obtained for only one out of the 53 (1.89%) masou salmon studied from the Kiso-gawa, which falls into the latter category above. As for the number of larval tapeworms occurring in each fish, the usual finding was between one and

five. According to the results that have been compiled by the author so far, the only second intermediate host of D. latus found in nature in Japan is the masou salmon Oncorhynchus masou. However, the question can still be asked if this is indeed the lone second intermediate host for these tapeworms here. There are many fish in Japan that are similar to Oncorhynchus masou: these include the chum salmon Oncorhynchus keta, the humpback or pink salmon Oncorhynchus gorbuscha, the coho salmon Oncorhynchus kisutch, the sockeye salmon Oncorhynchus nerka, Page 36 the rainbow trout Salmo iridius, the trout Salmo perryi, riverine fishes in the genus Hucho, char in the genus Salvelinus, sweet smelt in the genus Plecoglossus, etc. Although the author's investigation of these types of fish did not involve very large sample sizes, it remains true that, in every case, negative results were obtained. It must be recognized that there is room for further research on parasitism in these species. As will be discussed in subsequent chapters, fishes other than masou salmon can also be caused experimentally to be intermediate hosts of D. latus. That is, since the author was able to experimentally cause grass carp (a variety of Oncorhynchus masou) and rainbow trout to be parasitized with the plerocercoids of D. latus, it can be said that these two types /p. 23 can serve at least temporarily as second intermediate hosts of this tapeworm.

Chapter 3. Morphological Observations an Plerocercoids

Section 1. The Morphology of Plerocercoids

Shape Plerocercoids have a somewhat flattened, string-like shape; they are milk-white to yellowish-white in color, and their nerves may have a luster similar to that exhibited by silk thread. However, in some plerocercoids the muscles may have a slightly yellowish tint. Structurally they are simple, and no proglottids are observed. When the plerocercoid contracts, numerous transverse folds are produced. The plerocercoid's body moves in two manners, by expansion and contraction and by writhing or vermicular motion. The measurements that were made of the plerocercoids' dimensions are shown in Table 12. As can be seen from these data, the plerocercoids were found to range in length from 3.0 to 15.0 mm when they were in a contracted state, their average length being 6.33 mm, while their breadth fell between 1.0 and 2.0 mm, the average value being 1.49 mm. When the plerocercoids were extended, they showed a length of 10.0 to 40.0 mm, the average length being 21.89 mm, and a breadth of 0.3 to 1.0 mm, with Page 37 an average value of 0.52 mm being calculated. Thus the size of the plerocercoids when extended can be up to two to five times as great as the size when they are contracted. As for the thickness of the plerocercoids, when contracted they were found to be about one-half as thick as broad; for example, a larva with a breadth of 1 mm had a thickness of roughly to a thickness of 0.55 mm. However, when the plerocercoids are extended their [shape] may be quite variable. In this state their head region is pear-shaped, and dorsoventrally they possess a pair of deep bothria. Therefore, the layer situated between the two bothria accounts for no more than one-third of the diameter of the plerocercoid's body.

Structure The surface of the plerocercoid's body is evenly covered with a glass-like membrane that evidently has no structure; this is a cuticule. The thickness of this cuticule ranges from 0.0075 to 0.1 mm. Although the subcutaneous muscle fibers are very thin, two layers, one with an annular shape and the other extending longitudinally, can be barely distinguished. The [extent] of this muscle layer varies according to the size of the plerocercoid, as it becomes rather markedly developed in the larger ones. Subcuticular cells (or "Subcuticularzellenn) are irregularly arranged and small in number. The next major section of the plerocercoid's body is formed by longitudinal muscle [fibers] that are arranged in a bundle and traverse the middle layer [of the plerocercoid's

body] and by disorganized, transversely arranged muscle fibers. Moreover, numerous parenchymatous cells (or "Parenchymzellenn) are also present, forming a reticular interstitial [tissue]. The longitudinally disposed muscle fibers are well- developed and appear large and rope-like, whereas the transverse muscle fibers

are conspicuously fewer in number than the longitudinal ones. Although not very many of them are found, some large cells are observed among the parenchymatous • cells. These large cells, which are of diverse shapes, have comparatively small Page 38 • nuclei that are situated within abundant protoplasm. It would appear that these cells should be classified as being a type of glandular cell, but this inter- pretation certainly remains open to debate. In addition, a another type of cell that stains darkly with eosin can also be Observed. These cells are dispersed and few in number. Although some calcareous bodies are also present, they are dispersed here and there in all of the plerocercoids. When these calcareous bodies are treated with Koch's* stain and with Reru**'s stain, they exhibit an unusually beautiful color. The shape of these bodies is spherical to irregularly ellipsoi- /p. 24

dal, and their diameter has been computed to range between 0.0075 and 0.01 mm. Furthermore, [a pair of] longitudinally disposed tubular cavities can be seen, each of them [extending a distance] of approximately one-fourth of the plero- cercoid's body. The walls of these tubes are thin and covered with cuticule, and within the cuticular layer some subcuticular cells are arranged parallel to one another. These should be regarded as the main excretory tubes. The diameter of the lumen of the tubes is 0.01 mm. Circular or elliptical cavities can be observed here and there around the exterior of these two [tubes] when they are viewed in transverse section. These should probably be regarded as spedial types of transverse sections or oblique sections of the excretory ducts.

Section 2. The Site of Plerocercoids' Parasitization of Masou Salmon When investigating the sites within the bodies of masou salmon where plero- cercoids of Dibothriocephalus latus parasitize this fish, it should be borne in mind that the biological characteristics of the plerocercoids and the route of

*Translator's note: A guess. The Japanese word here, "Kossa", appears to be an unorthodox way of romanizing Koch. **Translator's note: Japanese romanization of unidentified surname-that • sounds something like "Rail" or "Lail". Page 39 their migration from the first intermediate host are both very significant factors in resolving this problem. Not only this, but an understanding of these factors

is also essential from the standpoint of preventing infection with these /p. 25 tapeworms. Consequently, the author gave considerable attention to these aspects of the problem when he investigated it. Moreover, in spite of the fact that, according to Braun and other researchers, [D. latus] shows a fairly high rate of parasitization not only in "the muscles but also in the viscera of European [fishes], only infections in the muscles were observed in the research reported by D14 . Ijima here in Japan. It must be considered an open question whether these difference in the research results is attributable to a difference in the inter- mediate hosts for this parasite in Japan and Europe. The author investigated the sites of infection in masou salmon that were positively found to be parasitized. The results of this study, in which 87 salmon

that carried a total of 98 plerocercoids were examined, are shown in Table 13. For convenience the author divided the fishes' muscles into two broad categories, dorsal and ventral muscle, and then further subdivided these into muscles at various regions: the head region, the neck region, the thoracic region, the dorsal region, the caudal region, the back of the abdominal wall, and the abdominal

wall. The data for 1922 indicate that eight plerocercoids were found in the muscles of the abdominal wall and at the back of the abdominal wall of the infected fish, three plerocercoids were found in muscles in the dorsal region, two in the neck region, and one apiece in the thoracic and caudal regions. Of the 38 plerocercoids investigated in 1923, 10 were dbserved to be located in the muscles in both the abdominal wall and the dorsal region; seven were found in the thoracic region, and seven also at the back of the abdominal wall; two were found in the • caudal region; and one in the neck region. One plerocercoid, moreover, was figured Page 40 to be free in the abdominal cavity of the fish. Of the plerocercoids examined here, two were found to have parasitized the fish at a site deep within it, practically contiguous to the backbone. In 1924 the infection sites of 18

plerocercoids were investigated; of these, seven were found in [muscles in] the dorsal region, five each in the abdominal wall and at the back of the abdominal wall, and one was in the thoracic region; all told, one of these plerocercoids appeared deep in the fish near the backbone. The infection sites of 27 plero- cercoids were examined in 1925; of these, 11 were observed in [muscles in] the dorsal region, eight in the abdominal wall, three at the back of the abdominal wall, one was free in the abdominal cavity, one was in the thoracic region, and three were in the viscera. Of the three plerocercoids found in the internal organs, one occurred in the pyloric appendage, one in the stomach wall, and one was underneath the intestinal serous membrane. Summarizing the data gathered

over the four years of the above study, we find that 31 of the plerocercoids were found in muscles in the dorsal region, 29 in the abdominal wall, 17 at the back of the abdominal wall, 10 in the thoracic region, three in both the caudal region and the neck region, and three in the viscera; the remaining plerocercoid was presumed to be free in the abdominal cavity. These locations, that is,

indicate the sites of parasitization by these plerocercoids.

Furthermore, if we examine the data on the 93 plerocercoids that parasitized the fish within their muscles, we note that the majority of them infected muscle layers relatively close to the cortex; 56 of the plerocercoids fell into this category. In contrast, only a few of the plerocercoids - no more than two, in fact - were found to have infected the subcutaneous tissue directly beneath the cortex. Twenty-eight plerocercoids parasitized deep muscle layers, and seven • were found in the deepest layers of the muscle, that is, those near the backbone. Page 41 • The above results indicate that, although plerocercoids [of D. latus] do parasitize the internal organs of Japanese masou salmon, the principal site of infection in these fish is the muscles, and it is the muscles of the abdominal

wall and the dorsal region where the parasitization most frequently occurs. However, the masou salmon used in the author's research were ones that were examined several hours or days post-mortem. According to Mi*. Shotaro ITO's studies on the site of parasitization by liver flukes, the infection site may be considered to change with the passage of time; the flukes [normally] infect the Victim within

the bile ducts, but [as time passes] they gradually move from the peripheral bile ducts to the large bile ducts and the biliary passage. However, it does not appear to be very likely that bodies such as the plerocercoids of D. latus, which infect substantial muscles and which themselves are large in size, would shift in position after death occurs. The author is here regarding the infection sites that were noted in the above study to be the sites where the plerocercoids were located immediately before the fishes died, and he is confident that no difficulties will arise as a result of this assumption. Consequently, the effect that the elapse of time had on the position of the plerocercoids post-mortem will not be discussed in any special detail here.

Section 3. The State of Parasitization of Plerocercoids /p. 27 Within the Body of the Second Intermediate Host

Postscript. Tissue Changes That Take Place in the Host As a Result of Parasitization by Plerocercoids

The parasitization of masou salmon by D. latus plerocercoids can take many

diverse forms; by no means is it uniform. In some cases [the position of their infection] agrees with myomeres; in other cases they infect their victim within muscle bundles. Màny cases of D. latus infection are of the latter type,— More- Page 42 over, some plerocercoids appear to be in a state where they are extended for the most part but are also partially contracted; others may be curved, or bent two- or even three-fold, or shaped like the symbol "<". Or some plero- /p. 28

cercoids may extend only to a moderate degree, exhibiting a horseshoe shape, or dominating a large area by ringing their bodies like a snake, or twisting and coiling. Furthermore, when they are viewed through thin layers of muscle, these larval tapeworms characteristically display a distinct yellowish tint. We come now to the question of whether the plerocercoids are encysted. As

mentioned previously, Dr. Ijima did not observe any encystment of the larval tapeworms he discovered. In spite of this, however, the present author's investigations of a large number of fishes show that some [D. latus] plerocercoids definitely are encysted, even though such larvae are not very numerous. In the • author's research, 10.1% of the plerocercoids examined (i.e., 10 of them) were found to be encysted. Encysted plerocercoids were found in the viscera, too; of particular note here is that an encysted plerocercoid was even discovered in the pyloric appendage. Although hosts infected by plerocercoids do not always undergo the same

changes as a result of this parasitization, it may well happen that their muscle fibers will either be thrown into disorder or even severed as a result of the pressure exerted by the plerocercoids. Mbreover, muscle fibers in the vicinity of plerocercoids may be deficient in contractive substances or may deteriorate in strength, usually degenerating until they have a slightly beady* type of appearance, or degenerating to the point where vacuoles appear in some places.

These changes are believed to be [extensive enough] that they can be observed • in nearly every instance. In addition to these changes, however, minor bleeding *Translator's note: Literally, "seed"-type. Page 43 or cell infiltration may also be dbserved either around the plerocercoid or at a slight distance away from it; alternatively, connective tissue may proliferate in the vicinity of the plerocercoid, or in some cases cysts may be formed, or in other cases there may be a proliferation of connective tissue that extends in a radiating fashion among cords of muscle fibers that are centered around the plerocercoid's body. These degenerative changes or cell infiltrations appear to be especially pronounced tomard the posterior end of the plerocercoids; many cases have been observed where the changes or infiltrations are oriented in a direction that is believed to reflect the course of the [plerocercoid's] previous passage [through the tissues].

Chapter 4. Biological Observations Concerning [D. latus] Plerocercoids, Particularly the Resistance Exhibited by Them

If plerocercoids are placed in salt water, they will move about energetically. Two main types of movement by these plerocercoids can be distinguished: movement by expansion and contraction, and a vermicular type of movement. By expanding and contracting, the plerocercoids are able to extend their body length from two- to five-fold, and by this means they can move forward. This forward motion can be supplemented by undulating contractions caused by moving the anterior part of their body toward the rear or moving from the rear toward the front. Furthermore, as a result of vigorous movement of the plerocercoid's head and alteration of its shape, the bothria may expand or become narrower or irregularly shaped. These motions can be made very striking by heating the salt water to a suitable temperature. As for the resistance exhibited by plerocercoids, both Braun and Ijima observed that plerocercoids could survive in the flesh of fishes that had been packed in ice, and Braun and Shor reported that plerocercoids survived very well • Page 44 in the flesh [of fishes] that were pickled in brune or smoked. According to the results obtained in tests by the present author, [D. latus] plerocercoids were still very much alive two to five days after masou salmon flesh that they infected had been packed in ice; see Table 14. When the author makes reference here to fishes being packed in ice, he means that the abdominal cavity and body surface of the fish had been packed and covered with ice. In other experiments using the same type of method, the author observed that /p. 29 larval tapeworms were still moving actively two days after the fish flesh they

lived in had been steeped in brine, and they also were found to be alive in flesh that had been decaying for five days. As the above results demonstrate, plero- cercoids are fully able to survive for two to five days in fish flesh that has been packed in ice or pickled with salt under the conditions of the author's experiments. When plerocercoids were immersed in salt water or tap water and left at room temperature for three or four days, their bodies became inflated so as to appear vacuolated here and there, and gradually softened and disappeared from the posterior end onward, except for the head region, which remained living until

the very end. The softening and disintegration of the plerocercoid's body took place somewhat more rapidly in tap water than in salt water. However, it goes without saying that the room temperature has a significant effect in experiments such as the one above, with a warmer temperature making the softening proceed more rapidly. When [D. latus] plerocercoids were placed in 80% alcohol, 1% anhydrous alcohol, 1% formalin, or a 0.1% aqueous solution of mercuric chloride, their bodies immediately contracted and they died. Furthermore, when pleroceryoids • were placed in usanbaizun (a sauce consisting of sake, soy and vinegar) or soy • Page 45 sauce, their bodies also immediately contracted, but when they were removed from the sauce after 10 minutes and rinsed with salt water, they gradually began to move again. When a 2 cm thick chunk of fish meat that harbored plerocercoids was cut and then smoked over a charcoal fire to prepare smoked fish, viable larval tapeworms could still be observed after 5 minutes; when the fish meat, however, was smoked for 10 minutes, or was immersed in a boiling bath, all of the plero- cercoids perished. The fact that plerocercoids do display some powers of resistance, as indicated above, has certain implications for the Japanese cuisine and cooking practices. Now, if fish is eaten raw after it has been packed in ice or steeped in brine during a short period of storage in an ice house, or if raw fish is consumed after dipping in sanbaizu or soy sauce (i.e., as sashimi), any plerocercoids in it will not likely have been killed by these actions. The same, of course, holds true for fresh fish that is simply eaten raw. As a result, when fish that has been parasitized by plerocercoids is consumed in one of the above manners, the [person] will become infected with the Dibothriocephalus latus tapeworm. In

the case of incompletely smoked [fish] meat, too, plerocercoids of D. latus will not have been killed. However, it is evident from the above discussion that D. latus plerocercoids are killed when [infected fish] is boiled* for 5-10 minutes or is immersed in a boiling bath. Table 14 presents the results of only the main tests that have been conducted to examine the powers of resistance of

these plerocercoids. /p. 30

*Translator's note: Sic. Presumably the author meant "smoked" here. Page 46 Part III. The Growth of D. latus Plerocercoids in the Definitive Host

Chapter 1. Literature on the Definitive Hosts of D. latus Felix Platter* discovered D. latus in human beings in Basel. This discovery attracted the attention of researchers, since this was the first time these tapeworms had been distinguished from the genus Taenia. Subsequently, this parasite has come to be found frequently in humans, and as a result it has been known by many different names, until now it has come to be referred to as Dibothriocephalus latus. This tapeworm eventually was also found to be a parasite of various types of mammals other than man. Since Linne and Pallas first recorded a case of [D. latus] parasitism in dog, many other researchers have followed up their work with the discovery of other such cases, in Germany, France, Britain, Norway, Italy, Denmark, and so on; included among these workers are /p. 31 Siebold, Krabbe, Peroncito, Cobbold, Knoch, Haemdon, Braun, Galli-Valerio, Deffke, Kitte, Stefan van Ratz, Megnin, and others. At the present day Ercolani has published a paper referring [to this tapeworm] as Bothriocephalus canis, and Generali describes it as Bothriocephali; both of these researchers treat this tapeworm as a parasite of dog. Although no actual cases of cats having been parasitized by this tapeworm have been uncovered, Creplin maintains that he observed proglottids of D. latus that had been shed by a house cat in Kuraifusuwarudo**. Since the tapeworm that was found was very immature in its development, it was difficult to immediately identify it as belonging to D. latus. However, Creplin stated that the structure of the parasite was recognizably that of a D. latus tapeworm. Krabbe, moreover, also observed a tapeworm from a cat, and this tapeworm possessed a spearrshaped

*Translator's note: Inference; the text says Felix "Plater". **Translator's note: Japanese romanization of an unidentified place name. • Page 47 head and was 15-20 am in size. In Krabbe's view, this parasite belonged to D. latus. Leuckart, in his well-known work, noted that D. latus tapeworms not only showed very slow growth after being ingested by dogs and cats, but also underwent

slight changes as far as their size and structure were concerned, becoming smaller and somewhat degenerative in form. Here in Japan Dr. Yoshida has reported observing D. latus in lions, bears and jackals reared at the Ueno Zoo. However, he was only able to detect some strobilae, for in each case the head of the tapeworm was missing. In May, 1923,

the present author examined a tapeworm eliminated by a pet dog in Takayama, a town in Ono District of Gifu Prefecture. Moreover, he also investigated a tapeworm that was excreted by a bear in Nagoya. In both cases the author was able to confirm that the specimens were complete D. latus tapeworms. Subsequently Dr.

Ando reported that he had detected D. latus eggs in the feces of a dog near Ogaki City.

Chapter 2. Experimental Ingestion of Plerocercoids Obtained From Màsou Salmon Caught in the Jintsu-gawa

To verify that the plerocercoids detected in masou salmon from the Jintsu-gawa

were in fact those of Dibothriocephalus latus, it was necessary to go beyond mere morphological investigations and to have the plerocercoids enter the bodies of its definitive hosts to see whether they would grow into adults, that is, into [mature] D. latus tapeworms. Mbreover, by having the plerocercoids be experimen-

tally ingested, it was possible to make a further study of which animals serve as a definitive host for this tapeworm and to also learn more about the states of growth achieved by the parasite within the hosts' bodies and to investigate any differences that mgy characterize its growth in the different types of hosts.

With these goals in mind, the author conducted a study in which these plerocercoids • Page 48 were experimentally fed to various types of animals. The results of these experi- ments will be described below.

Section 1. Experimental Materials and Test Animals

The materials used in these experiments were plerocercoids removed from masou salmon that had been caught in the Jintsu-gawa and examined by the author during his annual visits to Takayama in Ono District, Gifu Prefecture. These plerocercoids had the morphological features described in Part II of this paper.

The ingestion tests were carried out in either of two ways, following the same procedures reported previously. In one method, the plerocercoids were immersed in salt water, and the ones that displayed good movement were then fed to the test animals, which swallowed them together with salt water. The other /p. 32 approach was to use plerocercoids that seemed to have stopped moving after being kept for a lengthy time in salt water but which remained alive, as shown by the fact that they once more began to move actively when directly stimulated or when [the water they were in was] heated. Plerocercoids were also fed to the test animals as is - i.e., as they occur in fish meat - together with the fish meat, or in some cases, depending upon the purpose of the experiment, the animals ate

plerocercoids that had been artificially severed so that only their heads remained. By means of these experiments it could be learned whether the plerocercoids were still able to develop into adult tapeworms under the conditions tested. In addi- tion to human beings, the test animals employed included dogs, cats, monkeys, guinea pigs, white rats, and chickens. In each case without fail the excrement of the test animal was checked before it ingested the plerocercoid[s] to see if any parasite eggs were present, and any animal that this preliminary test • indicated might pose a problem in this respect was removed from the study. • Page 49 Section 2. Results of Experiments in 1922

Experiment 1 (Dog No. 1) The plerocercoid used in this experiment was obtained from a masou salmon that was delivered to the author after having been packed in ice for five days. This plerocercoid was immersed in salt water for one day before it was fed to dog No. 1 on Mhy 5, 1922. At the time of the test this dog was one-and-a-half months old. The dog consumed the plerocercoid together

with salt water. Subsequently the dog showed no adverse symptoms, and daily examination of its feces disclosed no parasite eggs had been discharged. The dog was sacrificed* an July 11, and no parasite body was discovered on necropsy.

Experiment 2 (Dog No. 2) The two larval tapeworms (plerocercoids) used in this experiment were obtained from the same masou salmon described above.

41, These plerocercoids were ingested by dog No. 2 on May 6, 1922. On May 9 the dog vomited some partially digested material, and on May 16 it experienced a bout of watery diarrhea. However, examination of its stools failed to disclose the presence of tapeworm eggs. This dog subsequently became very weak and died on June 1. However, no tapeworms were discovered in its intestines when the

dog was necropsied. An Echinococcus parasite, however, was found. Experiment 3 (Dog No. 3) On June 3, 1922, two [normal] plerocercoids and a single half-crushed plerocercoid were fed for experimental purposes to dog No. 3. Several days later this dog experienced a bout of watery diarrhea, but no tapeworm eggs could be detected in its feces. Subsequently the dog's chain broke and it ran away. Thus the results of this experiment were incon- clusive.

Experiment 4 (Human, Case No. 1) (the author) On June 1, 1922, the author himself swallowed a plerocercoid together with salt water. Subsequent daily

*Translator's note: Inference; the text merely refers to its having died. • Page 50 examination of his stools revealed no sign that tapeworm eggs had been eliminated. Summary In the above experiments conducted in 1922, plerocercoids [identified as being those] of D. latus were ingested, in one case by a human subject, and in three cases by dogs. In each case either negative or inconclusive results were obtained, since no D. latus tapeworms could be detected. However, although the results of these experiments must be viewed as negative, some symptoms indicative of a gastro-intestinal response to the organisms were in evidence,

so that one cannot help but think that, at some stage of their growth, these tapeworms are destroyed under certain types of conditions and are absorbed by the victim's body. Section 3. Results of Experiments in 1923 Experiment 5 (Human, Case No. 2) (the author) On May 27, 1923, the author himself swallowed two plerocercoids together with salt water. In the evening on May 30, the author experienced abdominal pains and diarrhea, and these symptoms persisted for three days. Afterwards the author frequently had headaches, and was affected by cerebral anemia during his work. The author's stools were examined

daily using the dilute hydrochloric acid ether* technique for egg collection, and on June 11, one or two D. latus eggs were detected in one of the specimens. Subsequently the number of eggs in the stools was observed to increase gradually. However, the number of eggs that were present showed marked variation at times, so much so that, even though the egg-collection procedure was followed in its

entirety, practically no eggs could be detected, leading one to suspect that the parasite had been eliminated. After September 29, when the author experienced repeated instances of diarrhea that had been preceded by abdominal noises, part - II› of a tapeworm strobila was excreted. This strobila had a length of 85 am; the

*Translator's note: Literally translated. • Page 51 first proglottid was found to be 6.5 mm vide and 1.5 mm long, and the largest

proglottid was 7.5 mm wide and 3 mm long.' The eggs, the characteristics of the proglottids, the morphological features of the uteri, etc., were all consistent with those of D. latus. Innumerable brown eggs were found within the uteri. In the following year, on April 17, part of a tapeworm strobila - one that was missing a head - was again excreted, once more preceded by abdominal noises and diarrhea. This strobila was 2 m, 15 am in length and was found to contain

788 proglottids, with the largest of these proglottids measuring 5 mm in length

and 8.5 mm in breadth and the one at the anterior tip of the strobila /p. 33

being 6 mm wide and 3.5 mm long. This strobila, moreover, possessed a terminal segment at its posterior end. Furthermore, the author again experienced diarrhea accompanied by abdominal noises and pain an July 27, 1924. Afterwards a tapeworm

measuring 4 m, 19 am long was discharged. This tapeworm, which had a damaged head, posssessed 2,303 proglottids. The neck region at the anterior extremity of the tapeworm was 1.3 mm wide. Uteri could be seen with the naked eye, beginning

with a section that was 4.5 mm wide and 1.0 mm long. The largest proglottid

was 8 mm wide and 3 mm long. After July 27th no tapeworm eggs were discovered

in the author's stools despite repeated examinations of them. As for blood signs, the author's leukocyte count, in tests conducted on Màrch 20, 1924, was 5,550;

his red corpuscle count was 4,100,000; and his hemoglobin percentage was 62%, indicating that he had fallen into a somewhat anemic state, at least temporarily. On September 20, 1924, the.author's leukocyte count was 6,800, his red corpuscle count was 4,900,000, and his hemoglobin percentage was 82%. Therefore, the author is confident that the tapeworms in his body were probably completely discharged

*Translator's note: Literally translated. • Page 5 on July 27th.

Experiment 6 (Dog No. 4) On May 29, 1923, plerocercoids that had been detected in masou salmon were fed to this dog for experimental purposes. Than beginning on June 12, one or two eggs of D. latus were detected in multiple fields of vision using the dilute hydrochloric acid ether technique for egg collection After June 14 numerous tapeworm eggs were observed in the feces of this dog,

and these eggs were later used as test materials in culture experiments. However, in August of that year, while the author was away doing research on diseases caused by chiggers, the [tapeworm] that was thus grown died, so that it was no possible to investigate it in a live state. After a preliminary examination the tapeworm was placed in formalin and its abdomen was opened and inspected. This tapeworm, which possessed a head, was 12 am long. The scolex of this tape • worm measured 1.55 mm in length and 1.0 mm in breadth. The tapeworm had two bothria, and its terminal segment was 0.55 mm long and 3.0 mm wide. Eggs were not found in the uteri of the various segments. The general morphology of thi tapeworm was consistent with that of Dibothriocephalus latus.

Experiment 7 (Dog No. 5) On May 30, 1923, one plerocercoid that had infected a masou salmon was ingested by this dog, then on June 8 another plero cercoid was also fed to this dog. Eggs of D. latus were first detected in the dog's feces on June 14, using the [above] egg-collection technique, and eventually large numbers of these tapeworm eggs were being eliminated.

Experiment 8 (Dog No. 6) On June 8, 1923, two plerocercoids were fed dog No. 6. This was a dog that appeared to be developing a neoplasm on its pen that was similar those seen in breast cancer. A few tapeworm eggs were discovered when the [above] egg-collection technique was employed in examining the feces • of this dog on June 11, and from June 24 an large numbers of these eggs began

ea+ • Page 53 to be detected. Then, one day in August, while the author was away doing his research on chigger diseases, tapeworm proglottids were found in the dog's excrement. Although the author himself was unable to examine these proglottids, their morphological features were reportedly similar in every respect to those

of D. latus. Experiment 9 (Dog No. 7) One plerocercoid was also fed to dog No. 7

an June 8, 1923. The feces of this dog were inspected daily from then on, and on June 23 a small number of D. latus eggs were discovered using the egg-collection technique discussed above. Subsequent daily examinations of its stools revealed that the number of eggs being shed was steadily increasing. Together with the

eggs eliminated by dogs Nos. 5 and 6, these tapeworm eggs were used as materials for culture experiments. However, all three of these dogs escaped while the • author was away investigating diseases caused by chiggers, and their whereabouts are unknown. It is unfortunate that it was not possible to obtain adult tapeworms from the eggs excreted by these dogs. Nevertheless, since it was confirmed that each of these dogs did discharge tapeworm eggs, and that proglottids were excreted by dog No. 6, it can be stated that, in each case, positive results were obtained

in these experiments on the ingestion of plerocercoids. Experiment 10 (Cat No. 1) On May 29, 1923, the author fed one plero- cercoid to a young cat for experimental purposes. For the next three days this cat experienced repeated cases of diarrhea. Subsequent daily examinations of its feces failed to disclose the presence of any tapeworm eggs. The cat was sacrificed on July 1, and it was not found to have become infected with an adult tapeworm. - Experiment 11 (White Rat No. 1) On May 29, 1923, a white rat was fed • a single plerocercoid. However, this rat died While being transferred from the • Page 54 research facility. No parasitic tapeworm was discovered when the white rat was necropsied an June 11.

Experiment 12 (White Rat No. 2) On June 5, 1923, a single plerocercoid was also fed to this white rat. However, this white rat, like the one above, also died, and no parasitic tapeworm was discovered on necropsy.

Experiment 13 (White Rat No. 3) On June 8, 1923, one plerocercoid

was also fed to white rat No. 3. Nevertheless, this white rat perished, like

the other animals, while being transported from the research facility in a heavily loaded automobile that was travelling over a mountain road all day long. This white rat was necropsied an June 11, but no larval or adult tapeworm was found in its intestinal canal. Furthermore, although a special effort was made to find out whether the larval tapeworms might have penetrated below the skin or into the muscles or internal organs of the three white rats tested here, absolutely no evidence of this could be detected anywhere.

Experiment 14 (Guinea Pig No. 1) On June 8, 1923, a plerocercoid /p. 34 obtained from a masou salmon was fed to a guinea pig, and thereafter the feces of this animal were examined daily. No evidence of the elimination of tapeworm eggs could be discovered, and when a necropsy was performed on the guinea pig on June 29 no tapeworms were found to have parasitized its intestinal canal. A careful examination was made of the question of whether this larval tapeworm, like those of the genus Ligula, might have merely penetrated into the muscle or beneath the skin of this guinea pig. However, no plerocercoid could be detected anywhere. Experiment 15 (Chicken No. 1) On June 7, 1923, a plerocercoid that fully developed plerocercoid was immaturely developed was fed along with a more --- • to this chicken. However, necropsy of this chicken on June 23 failed to disclose • Page 55 the presence of these plerocercoids.

Snmmnry In 1923 plerocercoids collected from masou salmon that had

been caught in the Jintsu-gawa were fed to various test animals, including four dogs, one cat, three white rats, one guinea pig, and one chicken. One human

being also ingested these plerocercoids. The results of these experiments indicated that the one human subject and all four of the dogs tested had either been parasitized by Dibothriocephalus latus tapeworms or had been observed to discharge the eggs of D. latus in their excrement. Negative results, however, were obtained for the cat, and no evidence of tapeworm infection could be found in the intestinal canals of the three white rats, the one guinea pig, and the

one chicken tested. Neither was any evidence found that the plerocercoids, like the larval tapeworms of the genus Ligula, had penetrated beneath the skin or into the muscles of these animals.

Section 4. Results of Experiments in 1924 (Translator's note: Since the experiments discussed in this section are similar to those described in Section 3, the details have been omitted and only the summary has been translated.)

Summary In 1924 the author fed plerocercoids for to five dogs, AD. 35 two cats and one monkey. The results of these experiments were that three of the dogs and the one cat were found to have become infected with the D. latus

tapeworm. Dogs Nos. 9 and 11, however, died a short time after ingesting the

plerocercoids, and only immature forms of the tapeworm could be detected in them.

Dog No. 8 and cat No. 3 were found to have been parasitized by adult D. latus tapeworms, and these test animals were also observed to eliminate tapeworm eggs. Negative results were obtained for the monkey that participated in the f.eeding tests that year. Page 56 • Section 5. Results of Experiments in 1925 (Translator's note: Since the experiments discussed in this section are similar to those described in Section 3, the details have been amitted and only the summary has been translated.)

Summary In 1925 the author fed plerocercoids to nine dogs, one /p. 36 cat and one monkey. The results of these experiments were that six of the dogs and the single cat were found to have become infected with the D. latus tapeworm,

but negative results were obtained for two of the dogs and the one monkey tested that year. Experiments on Insertion of Plerocercoids Beneath the Skin and Within the Abdominal Cavity of Test Animals The question arises, Can plerocercoids of Dibothriocephalus latus survive

in the plerocercoid form within the bodies of warm- or cold-blooded animals other than masou salmon, particularly within their abdominal cavity or beneath their skin? When larval tapeworms of the type seen in the genus Ligula are inserted beneath the skin or into the abdominal cavity of such animals, the tapeworm is able to infect the host for a long time as a plerocercoid. Moreover, if these

larval tapeworms are fed to animals other than their definitive host, they immediately bore through the wall of the alimentary canal and enter the abdominal cavity. That they can infect such animals in their plerocercoid phase has already been experimentally confirmed by a number of researchers working in different localities; included among these is a study by the author (see Bulletin of

Pathology, Nagoya, Vol. 2, No. 2). Judging from the fact that the morphological and biological characteristics of the D. latus plerocercoid are similar to those of Ligula types of larval tapeworms, it may be possible that the sort of parasitism observed in the case of Ligula larvae might also occur with D. latus plergpercoids. • UNED FT ED SL TiON Fer TRADUCTiC.N NCIr+ R c.rra sew:Grave Page 57

As discussed in the sections above, when the author experimentally fed plerocer- coids to white rats (Nos. 1, 2 and 3), a guinea pig (No. 1), a chicken (No. 1), and cats (Nos. 1 and 2), careful inspections for the presence of plerocercoids beneath the skin and in the internal organs, muscles, etc., of the test animais one case of parasitism of this type. Therefore, it would failed to disclose even appear that D. latus plerocercoids do not bore through the alimentary canals and move to parasitize other parts of these animals' bodies. Here the author will discuss experiments in which plerocercoids of D. latus were inserted beneath the skin or into the abdominal cavity of various types of animais to discover what would happen to them next. The results of this study were as follows.

Experiment 16 (White Rat No. 4) On June 6, 1923, one immature plero- • cercoid was inserted into the abdominal cavity of this white rat. The rat, how- ever, died while being transported on June 10, and was partially eaten by another white rat. Examination of the parts of the rat's body that remained failed to disclose the presence of the plerocercoid.

Experiment 17 (White Rat No. 5) On June 6, 1923, one plerocercoid was inserted into the abdominal cavity of white rat No. 5. However, this rat

met the same fate as white rat No. 4 and the results of the experiment remained uncertain.

Experiment 23 (Chicken No. 2) On May 24, 1924, one plerocercoid was inserted into the abdominal cavity of this chicken, whose abdomen had been opened surgically. When a necropsy was performed on July 2, no plerocercoid was /p. 37 detected in either the abdominal cavity or in the subcutaneous muscles of this chicken. • Experiment 38 (Guinea Pig No. 2) On June 12, 1925, one plerocerCoid • Page 58 was inserted into the abdominal cavity of this guinea pig. When a necropsy was performed an July 6, no plerocercoid could be found anywhere within the test animal's body.

Experiment 39 (Goldfish) On June 12, 1925, [one] plerocercoid was inserted beneath the skin of a goldfish. Afterwards a small ulcer developed in the area where the skin of the fish had been stitched. The goldfish died on

June 23, but no plerocercoid could be found either in the muscles or beneath the skin of the fish on necropsy. Experiment 40 (Carp) On June 12, 1925, one plerocercoid was inserted into the muscle of a carp. This carp died on July 3 and a necropsy was performed. When a careful inspection was made of its muscles and abdominal cavity, as well as beneath its skin, no evidence that a plerocercoid was present could be found • anywhere. Although it was not possible to do many repetitions of the above experiments on account of the difficulty of obtaining good test materials, the results of each of the experiments condueted seemed to indicate that insertion of [D. latus]

the skin or into the abdominal cavity of the test animal plerocercoids beneath did not produce infection with this tapeworm. Section 6. Summary of Experiments We may now summarize the results that were obtained in the above experiments, in which plerocercoids from masou salmon caught in the Jintsu-gawa between 1922 and 1925 were fed to test animals. All told the experiments were conducted twice on a human being, as well as on 21 dogs, four cats, one guinea pig, three white rats, one chicken, and two monkeys. The human being used in the test was the author, who swallowed the plero- 11› cercoids himself and obtained negative results in 1922 but showed positive signs Page 59

• of parasitism in the 1923 trial, in which an adult D. latus tapeworm was observed

to have been shed on three occasions. Fourteen of the 21 dogs tested, became

parasitized by D. latus tapeworms, while negative results were obtained for four

of the dogs and inconclusive results for three of them. However, positive results

were found every year that the dogs were experimentally fed the larval tapeworms.

The tapeworms that were able to infect the dogs were believed to be essentially

similar, both in their state of growth and their morphology, to the ones that

parasitize human beings. Furthermore, the plerocercoids of D. latus that were

able to fully grow into the adult form were not only those that had been ingested

completely intact, but also ones that had been severed so that only their heads

remained.

As far as the cats were concerned, negative results were obtained in the • feeding experiments carried out in 1923, but every year thereafter it was found that the cats that had been fed these larvae became infected with the D. latus

tapeworm. That is, two of the four cats receiving the plerocercoids became

parasitized by these tapeworms.

Both of the feeding tests conducted on monkeys in 1924 and 1925 yielded

negative results, and no ensuing parasitism was found, either, in the feeding tests conducted each of these years on other animals, such as the guinea pig,

rats, chickens*, etc. On the other hand, the morphological similarity between

larval D. latus tapeworms and those of the type found in the genus Ligula suggested

the possibility that the former might be able to infect animals while still in the plerocercoid form before they switch hosts and parasitize their definitive

hosts. To investigate this possibility, the author conducted additional experi-

*Translator's note: Inference; the text says "birds", but only experiments involving chickens are discussed in the paper. Page 60 • ments in which larval [D. latus] tapeworms were inserted either beneath the skin

or into the abdominal cavity of various animals, namely, one guinea pig, two white rats, one goldfish, and one carp. However, negative results were obtained in all of these experiments.

Chapter 3. Growth of D. latus Tapeworms and Their Life- /1D• 40 Span Within the Body of Their Definitive Host

The first experiments in which D. latus larvae were fed to the definitive hosts (man, dog, cat, etc.) of these tapeworms were carried out by Braun, and subsequent ingestion tests were conducted by Parona, Zschokke, Rovelli, Grassi, Ferrara, Schroeder and Alessandrini, among others. Braun was also the first to publish a report on feeding experiments that were performed to study the growth of these parasites in the human body, the results of this study indicating that fully mature tapeworms required three to four weeks to develop, with the average daily growth of the tapeworms being between 23 and 31 proglottids* - a length, that is, of between 8.5** and 8.9 am. In the study by Parona tapeworm eggs were shed after 24 days had passed, whereas Grassi reported finding excreted tapeworm eggs four weeks after larval tapeworms had been experimentally ingested. Zschokke, meanwhile, stated that the average daily increases in length of tapeworms [in three cases studied] were 5.2, 6.2, an à 8.2 am respectively, whereas in one case an average daily increase of 2.2 cm was found. Ijima also performed a study in which [a] larval tapeworm [was] eaten, and he first noted the elimination of eggs on the 22nd day following its ingestion. The tapeworm showed an average daily growth of 66 proglottids, corresponding to a length increase of 5.2 to 8.2 cm per day.

*Translator's note: The text actually says 31 to 23; could there be a misprint here - i.e., was 31 to 32 intended by the author? • **Translator's note: Inference; the text says "85" here. • Page 61 The present author, too, conducted experiments in which he himself swallowed plerocercoids, and he found that strobilae were excreted approximately three times within a 426-day period. On the first occasion, which took place on the 125th day [following ingestion of the plerocercoid], the strobila that was shed

was 85 am long and consisted of 236 proglottids; the second time (200 days later) the strobila measured 2 m, 15 cm in length and had 788 proglottids, whereas the third time (another 101 days later) the strobila was 4 m, 59 am long and was made up of 2,397 proglottids. In total these strobilae measured 7 m, 59 cm in length and had 3,421 proglottids, and this corresponded to an average daily increase in length of 18 mm and the addition of eight new proglottids to the strobila per day. The experiments that the author performed on dogs indicated that the tapeworms developed a short time after the plerocercoids had been eaten. Twenty-four days after dog No. 13 had been fed a plerocercoid, a tapeworm that was 2 m, 77 am

long and had a strobila consisting of 1,716 proglottids was found. This amounted to an average daily increase of 71 proglottids and 115 cm. Twenty-four days after dog. No. 14 ingested two plerocercoids, a tapeworm that measured 89 cm in length and had a strobila with 1,053 proglottids was found; this corresponded to an average daily increase of 3.7 cm and more than 43 proglottids. The second tapeworm [excreted] was 73 am long and possessed a strobila with 1,042 proglottids; this worked out to a daily growth of 3 cm and over 43 proglottids. The tapeworm that grew in dog No. 22, meanwhile, was 2 m, 25 am long by the 40th day after the plerocercoid had been eaten, and had a strobila with more than 672 proglottids (the scolex was missing, however), indicating an average growth of more than 16 proglottids and 5.6 cm per day. Fifteen days after dog No. 19 ingested a plerocercoid, a

strobila with a total length of 1 m, 25 am and 738 proglottids appeared; this ob Page 62 amounted to an average daily increase of 8.3 am and 49 strobila proglottids. These results are shown in Table 16. Summarizing these data, we find that these tapeworms exhibited an average daily growth of 1.8 to 11.5 am in length and 8 to 71 proglottids, with the length of the strobila usually increasing between 40 and 50 segments per day. The reproductive organs of these tapeworms, further- more, developed to maturity quickly. However, after sexual maturity was reached the rate of increase in the number of proglottids appears to have declined while the rate of increase in the length and breadth of the proglottids seemed to be accelerated. Looking next at the number of days that passed between the time larval tapeworms were ingested and eggs were excreted, we note that 14 days elapsed in

the case of the human being tested (the author), while the figure in /1) . 41 • the case of the dogs tested was 14-17 days, usually being 14 or 15 days. There- fore, it is the author's opinion that D. latus takes approximately 14 days to develop into an adult tapeworm and release eggs. If we compare this to the views advanced by previous researchers, we find that this indicates a much more rapid rate of growth than previously indicated for D. latus. This discrepancy probably can be accounted for by the fact that, after the author swallowed the larval tapeworms, daily examinations of his stools were made using an accurate egg- collection technique. As a result, this should have made the author's study

more accurate, at least as regards the number of days that elapsed between the time that the author became infected with the tapeworm to the time that its eggs were shed. It would thus appear that D. latus tapeworms have a comparatively short residence time within the bodies of their hosts. The results of the author's - 41› the parasites experiments seem to indicate that, without any treatment being given, Page 63

• were completely rejected from the human subject's body within In the 425 days. case of the dogs tested, the tapeworms survived, without exception, for only a short period of time, as [the dog] either died or the tapeworms were discharged,

in nearly every case, within 12 months of the time [the plerocercoids had been

eaten]. Mbreover, this parasite is believed to survive for an even shorter length

of time in cats. If we look at the literature on the duration of this tapeworm's

stay in human beings, we find that Bremser reported a case of D. latus infection

that lasted for 15 years in someone who came from Canton, and H. Schapiro described a case where a person had been parasitized by D. latus for as long as 43 years. However, the author believes that a more reasonable explanation of the above cases would be that the victims had been repeatedly parasitized. The author

can recall the case of a child from Ichinomiya that he examined and dewormed.

This child, who was about . 9 years old, had excreted tapeworm strobilae on several occasions over the previous three years, and it seems probable that the child had ample opportunity to be reinfected during this period. Even if this

parasite is able to survive in the body for a long time, it does not appear to be likely that it could go on for several years. The reason that D. latus, a

hooked type of tapeworm, has a shorter life-span than hookless types of tapeworms could be that, in essence, the organ of attachment of this parasite is more poorly developed than that found in Taenia tapeworms, for D. latus is only equipped

with two incomplete bothria. Moreover, there are no structures in the vicinity

of these bothria that can properly be referred to as suckers. When the author examined this region of the tapeworm in a histological study, he observed that

the muscle layers surrounding the bothria appeared to be somewhat more developed than those elsewhere. In spite of this, however, it was impossible to avoid 11, the conclusion that these bothria were obviously incompletely developed, and • Page 64 that even if the tapeworm were to attach itself to the intestinal wall, it could be readily dislodged and eventually eliminated from its host by even a relatively minor adverse event. Of course the author does not go so far as to suggest that the reason cited above is the only factor that plays a role in the short life-span of D. latus.

Chapter 4. The Author's Observation of Cases of Animals /p. 42 That Have Been Naturally Parasitized by D. latus The question of which animals serve as hosts of D. latus in nature is an important one to explore if we are to understand how this parasite is distributed. Accordingly, the author undertook a study to find out the extent to which domestic animals such as dogs, cats and chickens were parasitized with D. latus in the town of Takayama in the Hida region, where, as discussed above, infection with • this tapeworm is widespread. In this study, in which infection was diagnosed by examining the stools of the animals, two tapeworms were unexpectedly shed by one infected dog. Examination of these two tapeworms disclosed that both of were adult D. latus specimens that possessed a distinct scolex. In addition, stool examinations were performed on wild animals kept at the Nagoya Zoo, with two lions, one leopard, three bears, one camel, two foxes and two wolves being included in the study. A brown bear (Ursus arctos L.) was found to be infected with D. latus, and two of these tapeworms were obtained when the bear was dewormed. These tapeworms were 1 m, 50 cm and 1 m, 65 cm long respectively, with the maximum breadth of the strobilae being 15 mm and their maximum length 1.5 mm. The lion[s], the leopard, and a tiger* were discovered to be infected with Dibothriocephalus

*Translator's note: Sic. The tiger is not mentioned above as having been • one of the animals studied. Page 65

decipiens, but no D. latus tapeworms were detected. Chapter 5. Summary of Part III (With Special Reference to the Definitive Hosts of D. latus) The foregoing part of this study indicated that, based on their morphological

features, the larval tapeworms that the author detected in masou salmon from

the Jintsu-gawa should be considered to be plerocercoids of Dibothriocephalus

latus. The author also showed that adult D. latus tapeworms could be obtained from human beings, dogs and cats that had eaten these plerocercoids in experiments,

thus demonstrating that the plerocercoids were D. latus larvae. From 1922 to 1925 the author carried out experiments in which plerocercoids obtained from masou salmon caught in the Jintsu-gawa were experimentally ingested by dogs, cats, guinea pigs, white rats, chickens, monkeys, etc., as well as by a human subject. The human subject was the author himself, who became infected

with the adult tapeworm after swallowing a plerocercoid. That is, the results of these experiments clearly bear out the fact that human beings are the most

common final host of D. latus in nature. A total of 21 dogs took part in the experimental feeding study. Of these,

14 were confirmed to have become infected with D. latus. The D. latus tapeworms that parasitized the dogs were inspected to determine the extent of their growth and their morphology, examining, for instance, the number of days that passed from the time the plerocercoids were eaten to the time that eggs were shed, the the strobila's rate of increase, the length of the tapeworm, its morphological features, etc. This study showed that, as far as the above respects are concerned, the tapeworms that parasitize dogs are not significantly different from those • that infect man. Absolutely DO evidence was found to support the contention that this tapeworm's growth and morphology are poorly developed in dogs, /p. 43

,• Page 66 which is a theory that Leuckart advanced in his well-known work. It should be mentioned here, however, that the intestinal canal of dogs is shorter and also narrower than that in human beings. This fact may account for the fact that the life-span of D. latus appears to be briefer in dogs than in man. This is shown by the author's finding that not even one of the dogs used in his experiments remained infected by this tapeworm for a full year. In each instance all of the tapeworms were eliminated within a matter of months, whereas D. latus in many cases is able to survive for a far longer period of time in humans. There- fore, it goes without saying that the tapeworms shed by human beings are larger than those shed by dogs. In spite of this, though, there is ample evidence that, in many different respects, no major difference exists between the D. latus tapeworms that parasitize man and those that infect dogs; these respects include • the stages of growth they pass through between their plerocercoid phase and their adult phase, their condition at a given period of growth, and their morphology. Dogs, of course, have been shown in experiments to be a suitable definitive host for D. latus. The author confirmed that [dogs also are D. latus hosts] in nature, as he observed that two of these tapeworms were eliminated from a dog raised by people in Takayama, a town in the Hida region, in May, 1924; the fact that D. latus parasitizes dogs has also been mentioned previously in the literature, as

discussed in Chapter 1 of Part IV of this study. Consequently, although dogs, under natural conditions, cannot be considered to be as common a final host of D. latus as man is, the explanation for this would seem to be two-fold; i.e., they have fewer opportunities to eat raw masou salmon, and the tapeworms are discharged from their bodies more rapidly than when human beings are infected.

As far as cats are concerned, two of the four that ingested plerocercoids • in the author's experiments were confirmed to have become parasitized by adult • Page 67 D. latus tapeworms. This finding demonstrated that cats, too, are a definitive

host of D. latus. The life-span of this parasite in cats, moreover, appeared

to be even shorter than in dogs. As a result, even though cats are a definitive

host of D. latus, they cannot be regarded as being as suitable a host for these

tapeworms as man. Larval tapeworms were also fed in these experiments to monkeys,

guinea pigs, chickens*, rats, etc., but not even one case of infection with an

adult tapeworm could be demonstrated. It is probably safe to say that none of

these animals can serve as a definitive host for D. latus, at least within the

range of conditions used in the author's experiments.

We will now consider the question of whether carnivorous animals other than

dogs and cats may frequently be definitive hosts of this tapeworm. As was men-

tioned above, the author has confirmed that D. latus can also parasitize bears,

and Dr. Yoshida reported that he observed 12 meat-eating animals at the Ueno

Zoo that were infected with D. latus, as he obtained headless strobilae of these

tapeworms. Based on these results, it appears probable that there are cases

where bears as well as other carnivores serve as a definitive host of this

parasite.

In addition, the author inserted larval tapeworms beneath the skin or into

the abdominal cavity of chickens, guinea pigs, white rats, a goldfish and a carp

to investigate whether they were able to infect their bodies for any length of

time under such conditions. However, negative results were obtained in all of

these tests. Thus there was absolutely no indication that D. latus larvae resemble

Ligula types of tapeworm larvae in being able to switch hosts, i.e., in having

the ability to infect an animal that is not its definitive host for a lengthy • period of time while still in the larval state. *Translator's note: See note on p. 59 of the translation. Page 68 Part IV. Experimental Studies on the First Intermediate Hosts of D. latus Chapter 1. History of Research on Whether There Is a First Intermediate Host of D. latus As was stated above in discussing the life history of D. latus, Braun and

other researchers discovered that an intermediate host was required by this parasite. However, one question that remained to be solved was whether only one intermediate host was necessary in its life history, which extends over many years; that is, are both a first and a second intermediate host required by this tapeworm? Although some researchers, such as Knoch, rejected the suggestion

that a first intermediate host exists for D. latus, Braun, Leuckart, Schauinsland and other scholars conjectured that there is a first intermediate host for this parasite, in view of the uniformly negative results that were obtained in experi- ments in which D. latus eggs or its six-hooked larvae were fed to fishes. They suggested that some invertebrate may serve in this capacity for D. latus. More

recently, Peiper (1910) and Janicki (1917) and Rosen conducted experiments in which eggs and larvae [of this tapeworm] were fed to Esox lucius, Perka fluvi- atilis, etc., in the case of the former two researchers, and to Leucinus alburus, Abramis, in the case of the latter worker. In each of these tests negative results were obtained. In 1919 Janicki and Rosen, as stated in the Introduction, undertook a study on the life history of Dibothriocephalus latus in Switzerland, and came to the conclusion that Cyclops sternuus and Diaptomus gracilis were the first intermediate hosts of this tapeworm. The pathbreaking work of these two men greatly illuminated the multi-year life history of D. latus. In their research they cultivated D. latus eggs until larvae were obtained, and then placed these larvae together • with various aquatic animals in the same environment. AS a result, it was found • Page 69 that these larval tapeworms showed unmistakable growth in the body cavities of only the two species mentioned above, taking on the so-called "procercoidu form. These researchers next confirmed that when these [procercoids] were fed experi-

mentally to Esox lucius and to the burbot Lota vulgaris, they penetrated into their stomach walls and migrated into their muscles, where they developed into plerocercoids. It was at this point that Janicki and Rosen assumed Cyclops sternuus and Diaptomus gracilis to be the first intermediate hosts of D. latus. In April, 1919, the author also began studies on the life history of this tapeworm. This research was undertaken completely independently of Janicki and Rosen, as it was only later that the author saw the results they had published. However, none of the species believed to be the second intermediate hosts of this tapeworm 110 in Europe - i.e., Esox lucius, Lota vulgaris, etc. - occur in Japan, and masou salmon , which is thought to be its second intermediate host in Japan, are not found abroad. Thus noting that the second intermediate hosts of D. latus cited in their study were different from the species that plays that role in Japan, the author considered it an open question whether this tapeworm's first inter- mediate hosts here were in fact the ones that Janicki and Rosen discovered. Furthermore, the latter researchers only used in their experiments Cyclops and Esox lucius, etc., that had been collected from their natural habitats, and they only pursued their studies to the point of confirming that larval tapeworms that had developed in the body of Cyclops penetrated the stomach wall of Esox lucius. Yet, in spite of these limitations, they immediately jumped to the conclusion that this finding could clarify the entire life history of D. latus. In fact, however, it can be questioned whether the results of their work cari be said to 11› apply under all conditions. That is, it is very difficult to determine /p. 45 whether the Esox lucius and Cyclops that they used had not already been infected • Page 70 with this tapeworm, so that the inescapable conclusion is that further confirmation has to be provided for the statement that the larval tapeworms that entered into the stomach wall [of Esox lucius] directly developed into plerocercoids. Not

only this, but species in the genus Cyclops are thought to serve as the inter- mediate hosts of several other parasites in addition to D. latus, and it is not an easy matter to distinguish between other tapeworms and D. latus during their larval stages. Consequently, the author believes it is most unfortunate that

Janicki and Rosen performed their experiments using Cyclops and Esox lucius that

had been obtained from nature, for this left considerable doubt about certain points in their study. To date the following copepods have been described as serving as intermediate or first intermediate hosts of parasites. In 1869 Fedschenko discovered that

Cyclops is an intermediate host of Filaria medinensis, then in 1878 Grube found

larval tapeworms in the body cavity of Cyclops serrulatus, stating that they should probably be regarded as larvae of Taenia torulosa. These facts have already been known for a long time. More recently Nybelin (1919) discovered larvae of

Schistocephalus solidus, C.F. Müller, that showed a certain degree of development

within the body cavities of Cyclops bicuspidatus and Cyclops serrulatus, and he

also found numerous cysticercoids in Cyclops viridis jurine, reporting that they were most likely Cyathocephalus larvae. Janicki (1920), moreover, has stated that larvae of Ligula intestinalis exhibit some growth in the body cavity of

Cyclops, and Okumura has reported that Cyclops leuckartii is the first intermediate host of Dibothriocephalus decipiens. Thus, in order to determine the first intermediate host that Dibothriocephalus latus has in Japan, and to make up for the shortcomings in the experiments-by

• Janicki and Rosen, the author continued his research on this tapeworm, hoping • Page 71 to gain a fuller understanding of its life history by carrying out the studies described below.

Chapter 2. Cultivation and Growth of [ D. latus] Eggs

That the eggs of Dibothriocephalus latus grow in water, giving rise to a six-hooked larvae, was noted by Knoch, Leuckart, Berutolus, and Schubart, among others, and has also been reported by Schauinsland on the basis of research results. In view of this, the author will only summarize the development of D. latus eggs and will give no more than a brief account of his observations on its six-hooked larvae, etc. The materials that the author used in his egg-culturing experiments were eggs that had been obtained by either of two methods. That is, they were either eggs that were naturally released from the tapeworm's strobilae when these

strobilae, which had been shed or obtained by necropsy, were placed in water; or they were eggs that had been collected from feces. When eggs were collected by the latter method, the stools were mixed with a large volume of water and left for one or two days, with occasional stirring, before being filtered and further [rinsed] with water a number of times. No significant differ- /p. 46 ence could be found between the eggs raised by the two methods, either as regards their cultivation or their growth. The eggs were placed in a Petri dish that contained a small amount of water, and were then either left at room temperature or transferred to an egg incubator. It appeared that the optimal temperature for [the growth of these eggs] in the incubator was 28-30 ° [C]. When the tem- perature in the egg incubator rose above 32 ° or dropped below 22 ° C, either the growth of the egg would be affected or the hexacanth larva's emergence from the • egg would be impaired. Moreover, the egg's development would also be hindered if too much water were to be placed in the Petri dish. In this case it was the Page 72 • development and multiplication of influenza and other viruses that provided the biggest obstacle to the growth of the eggs. The eggs in [Petri dishes] where these [viruses] developed experienced impaired growth, and even if some of them

were to develop into six-hooked larvae, the latter often would be completely unable to liberate themselves from the egg and would gradually shrivel up and die. As a result, egg cultivation would frequently have to be abandoned before it had reached completion. When eggs were being cultured by the above methods, either in a 28 ° C incu-

bator or at room temperature during the summer, the egg cells would quickly begin to divide to produce a pair of daughter cells. One of these would then undergo further binary division, and within about a week it would reach the so-called mulberry stage.* The other daughter cell would divide more slowly, developing • into an oblate cell coated by a membrane and covered by an egg-shell. The resulting group of egg cells was observed to form a circular aggregation with the ova positioned in the center; viewed from the outside, this region appeared more transparent than the others, so that the author decided to provisionally designate this area as the "hyaline body". After one week the egg cells that formed this hyaline body began to differentiate, producing a cell aggregation that we can refer to as a larva and a row of cells forming a covering layer that surrounded this aggregation. By this stage of development the yolk cells had already become nutritive and, as a result, they were mostly consumed. This left the primitively developed body of the larva clearly in view through the layer of cells that enveloped it. After approximately two weeks six hooks, in the form

*Translator's note: This apparently is a term the Japanese use in connection • with the raising of silkworms. Page 73 of three pairs of hooks, could be plainly dbserved on the larva's body surface. The six-hooked larva that was thus formed had a spherical shape and measured

0.0325 mm in diameter. By this time fine cilia had begun to form on the cell

layer that covered the larva. Although sometimes the six-hooked larva emerged from the egg as early as the 14th day, it usually was free after about three weeks. As the above is only a rough summary of the larval tapeworm's development, this growth may take place either faster or slower than indicated above. In

some cases the six-hooked larva may bear some hooks as early as the 7th day of rearing, while others may not develop hooks until later than stated above. Generally speaking, the larvae growing inside the incubator developed rather well, while those growing under room temperature conditions seemed to develop more slowly. Those larvae that were raised at room temperature in July and August II› grew rapidly, fully attaining the six-hooked stage within two weeks, whereas those that were reared in May, June and September showed somewhat slower develop- ment. Although the egg cells that were cultivated [at room temperature] in

November and December were seldom observed to divide, in most cases the eggs

did not appear to have perished. Table 17 presents data relating the development of tapeworm eggs to the air temperature over a one-year period. In this table the average air temperature observed each month in the author's laboratory is compared with the results of the rearing experiments that were then being conducted, and a similar comparison is made with respect to the average daily

maximum and average daily minimum air temperatures for those months. /1). 47 Furthermore, various "media" were tried in this egg-cultivation study. It was found that eggs that had been treated with a disinfectant developed more or • less the same regardless of whether tap water or salt water was employed. [-in the Petri dish]; it can thus be assumed that Dibothriocephalus latus eggs grow Page 74 similarly in freshwater and sea water. The eggs showed somewhat poor growth in a 5% aqueous solution of sodium bicarbonate, as only some of the eggs developed into six-hooked larvae. Although most eggs that were exposed to direct sunlight

died, some were still able to develop, giving rise to the hexacanth larva or oncosphere" with subsequent rearing. However, egg development completely stopped when the eggs were placed in 1-10% aqueous solutions of hydrochloric acid, 1-5% Goto "Deshin" solution*, 1-5% caustic potash solution, 1-3% carbolic acid solution, and 4-10% formalin. In these cases some of the eggs shrank, others became vacuolated, and still others gradually dissolved; eventually most of the eggs in the above solutions died, although there was some variation in the rapidity of their deterioration. The six-hooked larvae that did grow had a diameter of between 0.0275 and

0.035 mm and possessed a 0.0025 mm [thick] covering layer. On the surface of their bodies were six hooks that were 0.0075 mm long; spines were observed on the hooks, over an area accounting for one-third of their size. These hooks were somewhat curved. The six-hooked larva occupied a position near the covering of the egg, and gradually began to move by expanding and contracting. Each pair of hooks could be seen to be moving in a revolving or rotating manner, either by themselves or in tandem. Eventually these fully developed six-hooked larvae moved out into the water in the dish. That is, they opened up the egg's covering and emerged with an amoeba-like motion, and the long, delicate cilia now flourish- ing on the surface of their bodies became active as they started to swim, their

bodies themselves becoming somewhat altered and rotating in the process. During this six-hooked larval stage, moreover, the larvae themselves undertook their

-- • *Translator's note: Unidentified; could be a trade name in those days? L';‘!i:l1..'il.TE,0 71;`-''.i.•''''' '`.1-1 Di,/ Li 'Ti' Tr.l:\'''''''';'"Aït'•1/4.41.: «Fi_c'Ir'.:ç...)--;>':.;,;:::,1 For infe:•,•rti:?..,.f. ior! only ek''''';').' 1:(;:Je- s' riferrral•l•- - ■ TRADUCW,YA1 N(...)isû RE`•!;:!.‘L. ' '''' l'euietnete Informetion eeukrriei-it Page 75 vigorous expanding and contracting motions within the covering layer, with the end that possessed the hooks being especially active in this regard. The six- hooked larvae then gradually developed to the point where their diameter reached

0.075 mm. At this point the six-hooked larvae would seek out an intermediate host in an effort to parasitize it. If, however, no suitable host happened to be present, the larvae's motions would gradually abate, and then they would sink to the bottom of the water and barely move at all. Subsequently their cilia fell off, and they eventually died. Here it can be mentioned that the author still has made no attempt to ascertain whether calcareous bodies develop on the ciliated larvae. However, the author did examine six-hooked larvae that had been left alone for a long time and discovered that calcareous bodies had formed within the bodies of some of them. These calcareous bodies were not very numerous, only /p. 48 three of them being found. Some cases were also observed where calcareous bodies formed when a six-hooked larva failed to encounter an appropriate intermediate host; this provided the larva with a sort of durability that increased its powers of resistance, thus enabling it to live longer.

Chapter 3. Experiments To Determine Whether [D. latus] Has a First Intermediate Host, With Special Emphasis on the Growth of the Larval Tapeworm Within the Body of the First Intermediate Host

Section 1. Experimental Materials and Methods

The six-hooked larvae of Dibothriocephalus latus that were used in this study were ones that had been produced by cultivating tapeworm eggs. These eggs had been taken either from feces or from strobilae which had been discharged by the author himself or by dogs that had experimentally ingested larval tapeworms collected from infected masou salmon coming from the Jintsu-gawa. [Two types Page 76 of six-hooked larvae] were employed in these experiments; those that were still enclosed in their eggs comprised one type, and those that had naturally emerged

from their eggs formed the other type. These six-hooked larvae were either fed on an experimental basis to fishes, or were placed together in the saine habitat with small aquatic animals. However, the fishes that were employed here were ones that could serve as a second inter-

mediate host of D. latus - i.e., juvenile masou salmon, grass carp, and rainbow trout, and only juveniles that the author had painstakingly produced by artificial hatching were used. (These juveniles will be discussed further in a subsequent chapter.) Although the number of fish employed in these experiments was regret- tably small, the research still made it possible to remove any doubts that may have existed with respect to the question of whether the test animals could become • infected in nature. These fishes, moreover, were fed the six-hooked larvae by means of pipettes.

Some of the small aquatic animals that were used came from Takayama in Ono District, Gifu Prefecture, and others had been captured from ponds in the suburbs of Nagoya. The majority of these aquatic animals, however, had been raised;

that is, after April, 1924, all of them were obtained by artificial hatching. The technique used was to dig out a small water hole in the soil and spread clay over its sides and bottom, and then place a small aquatic animal, usually a copepod, into the hole and allow it to lay eggs. Later the water in the hole was be removed and left to sit for several days. The small aquatic animal that had inhabited the hole was allowed to die at this point, and then, when water was again placed in the hole and soybean scraps were added and left for awhile, other copepods or other small aquatic animals would eventually hatch from the • eggs. During warm periods in the spring these animals could be produced-extremely Page 77 quickly and they would reproduce in abundant numbers. In addition, the small aquatic animals thus obtained could be considered, of course, to be free of natural

infection by Dibothriocephalus latus. AD. 49 The aquatic animals produced in this manner were placed together with six- hooked larvae in Petri dishes, which were then left to stand at room temperature. After a certain length of time had passed the small animals were examined under the microscope, using either crushed specimens or transparent specimens that had been prepared employing glycerol-gelatin or glycerol-formalin agar, lactic acid and carbolic acid or other types of clarifying agents, etc. In these exam- inations the author investigated the extent to which the six-hooked larvae had penetrated into the bodies of the animals and the extent of their growth following such penetration. • Section 2. Experiments on the Ingestion of Six-hooked Larvae by Fish If Dibothriocephalus latus does not require a first intermediate host, then its six-hooked larva should be able to directly infect the fishes that serve as hosts for the plerocercoid of the species. However, as was discussed in Chapter 1 of this part of the author's work, experiments involving the feeding of six- hooked larvae to fish have already been performed by a number of researchers, including Braun, Leuckart, Schauinsland, Peiper, Janicki and Rosen, and in each instance negative results have been obtained. The author, desiring to gain a more detailed understanding of the recent pronouncements on this subject, con-

ducted his own research using juvenile grass carp and rainbow trout that had been artificially hatched so as to avoid any concern over the possibility of their having been naturally infected with D. latus plerocercoids. These test fishes were experimentally fed either six-hooked larvae or eggs that contained six-hooked larvae. The following results were obtained in this study. Page 78 II› Experiment 1. On June 5, 1924, six-hooked larvae that had emerged from their eggs were fed to two grass carps. When the fishes were necropsied on July 8, no evidence of infection by the larval tapeworms was Observed. Experiment 2. On July 8, 1924, [a ] six-hooked larva was experimentally fed to a grass carp, but this fish, too, failed to become infected with a plero- cercoid. Experiment 3. On August 30, 1924, a number of six-hooked larvae were fed to two rainbow trout that had been artificially hatched. However, when these trouts were necropsied on October 19, it was impossible to find evidence that they had been parasitized by plerocercoids.

Experiment 4. On September 16, 1924, eggs that contained larval tapeworms were fed to two rainbow trout that had been artificially hatched. One of these trouts was necropsied on October 19, the other on December 2. However, in both cases, no evidence of infection with plerocercoids could be found. For convenience the above results have been summarized in Table 18. The foregoing experiments yielded completely negative results. The /p. 50 question of whether the fishes that the author used in these tests - i.e., grass carp and rainbow trout - can serve as hosts for the plerocercoids of D. latus - will be addressed later (see Chapter 5). Nevertheless, if we simply look at the negative outcome obtained in each of these experiments, we must conclude

that neither the six-hooked larvae nor the eggs of D. latus are able to directly

migrate into these types of fish and grow into plerocercoids. That is, it appears to the author that the six-hooked larva of D. latus may have to go through a certain stage of development before it enters a fish and attains the plerocercoid

form. Or, to put the matter another way, D. latus, regardless of the conditions,

cannot dispense with a first intermediate host. • Page 79

Section 3. Experiments on the Interrelationships Between Aquatic Animals (Other Than Cyclops) and Six-hooked Larvae [of D. latus] As was discussed in Section 2, the author, on the one hand, carried out experiments in which six-hooked larvae [of D. latus] were fed to fish and, on the other hand, also did research on the interrelationships between these six- hooked larvae and various aquatic animals, this latter study being based on the

assumption that an aquatic animal that serves as prey for fish would have to be the first intermediate host of D. latus if one were to be required. As mentioned in Section 1, the small aquatic animals employed derived from three types of sources; i.e., some had been caught near Takayama in Gifu Prefecture, others

were collected from ponds near the author's laboratory, and still others were ones that had been artificially hatched from [eggs deposited by] the above two types. The various types of aquatic animals studied included larvae of the mayfly, Cyclops, the Japanese water scorpion Laccotrephes japonensis, kidorasu*, and moina*, as well as mosquito larvae, kawaro*, different species of Daphnia, spiral shellfish, and other small river shellfish, etc. These aquatic animals were placed in a Petri dish together with six-hooked larvae that had completely emerged from their eggs, and were left for two or three weeks before being examined under the microscope. These experiments indicated that the six-hooked larvae were able to penetrate into the bodies of the Cyclops specimens and grow there, but

that was all: with every other aquatic animal tested, not even a single case was dbserved where the six-hooked larvae entered the body of the animal and developed. In these experiments, when the six-hooked larvae were either placed together with only Cyclops or with a mixture of aquatic animals including Cyclops,

• • *Translator's note: Unidentified Japanese names. • Page 80 the number of larvae would eventually diminish, so that eventually no six-hooked

larvae could be seen freely swimming about. Yet, in spite of this, no six-hooked larvae could be found developing within the bodies of any of the aforementioned aquatic animals other than Cyclops. Examining the above findings, it is evident that none of these [other] aquatic animals can be the first intermediate host of D. latus; Cyclops alone has been found to serve this role. Consequently, additional experiments with Cyclops were performed. The results of this research will be discussed in detail in a subsequent section.

Section 4. Cyclops in Japan /p. 51 Kokubo has carried out detailed research on the genus Cyclops as it exists

in Japan. The author's identifications of Cyclops species are based for the most part an Kokubo's study. A summary has been prepared of the features that were used to distinguish the many species the author detected in the regions where D. latus parasitism is epidemic. This will facilitate our gaining a better understanding of this tapeworm's first intermediate host. (Translator's note: Only the names of the species cited by the author are presented here; the descriptions of these species have been omitted.) 1. Cyclops sternuus Fischer 2. Cyclops serrulatus Fischer 3. Cyclops magnoctavus Cragin

4. Cyclops leuckartii Sars 5. Cyclops signatus Koch. 6. Cyclops frexopedum n. sp. 7. Cyclops soli n. sp. /p. 52 8. Cyclops phaleratus Koch. var. japonica n. sp. • Page 81 The author collected a number of different species of Cyclops from ponds, swamps and fields in Toyama Prefecture and in Gifu Prefecture near Takayama, as

D. latus infection is rampant in these areas. Using Kukubo's published work as

the source of species identifications, the most prevalent Cyclops species [in the above regions] are C. leuckartii, C. sternuus and C. serrulatus, and a sizeable number of C. magnoctavus, C. signatus and C. flexopedum are also found.

Section 5. Experiments on the Interrelationship Between Cyclops and Six-hooked Larvae [of D. latus]

The author's experiments in which aquatic animals were placed together with six-hooked larvae that had been raised from eggs were repeated several more times, but negative results were still obtained. On November 12, 1923, however, the author did succeed in observing larvae that had penetrated into the body cavity

of [a] "kenmijinkon - i.e., a Cyclops sternuus copepod. The morphology of these larvae had changed, as they had taken on an elongated ellipsoidal shape. A spher- ical body that possessed six hooks was attached to one end of the larvae, and this spherical body was connected to the rest of their bodies at only a small, narrowly constricted region. These [larvae] were expelled from the body of the

Cyclops by applying only mild pressure. Examination of them indicated that their body surface bore small spines for the most part and was also provided with an epidermis. The body substance of the larvae was observed to include 6 to 14 calcareous bodies, and the length of their bodies was 0.4 to 0.5 mm. When the experiments were continued to determine to what extent larval tapeworms that

penetrated the bodies of the Cyclops would grow as time passed, it was discovered that the spherical body that possessed six hooks and was positioned at one end

of the larva broke off from the main portion of its body and gradually shriveled

up, with the six hooks eventually becoming detached. At this time, however, • Page 82 the main part of the larva's body showed a further increase in length, reaching

0.5 to 0.6 mm long, and depressions which could be recognized as the beginnings

of bothria were dbserved. Subsequently no additional growth or alteration of the larva's body could be seen despite continued study for several weeks. The above experiments were repeated again so that more detailed observations could be attempted. It was discovered that, when six-hooked larvae were ingested

by Cyclops, the cilia in [the latter's]* alimentary canal disappeared anywhere from a few hours to a dozen or so hours afterwards, and only those larvae that had shed their covering layer could bore through the wall of the alimentary canal [of the Cyclops] and enter its body cavity. As for the mechanism of the larva's penetration through the wall of the host's alimentary canal, the motion exhibited

by D. latus in the hexacanth larval stage - i.e., an expansion-contraction type • of motion - was found to take place, with this motion being especially /p. 53 vigorous at the end where the six hooks are positioned. In view of this, the author believes that the hooks themselves play a very important role in the

process. The size of the larva at this time was no more than about 0.025 [mm].

However, one week later the larva had grown to between 0.08 and 0.1 mm, a cuticle had developed on its body, and some calcareous bodies, too, had formed. After about two weeks the larva took on a conspicuously elongated ellipsoidal shape, with one of its ends becoming constricted. The hooks became gathered together

in this area. The length of the larva's body reached 0.1 to 0.125 mm and its

breadth was 0.05 to 0.075 mm at this stage, and the calcareous bodies had increased in number. The larva continued to grow from this point, attaining a length of

0.35 to 0.45 mm, while the constricted area became increasingly noticeable, with the part where the hooks were located becoming spherical and exhibiting only a

• *Translator's note: A guess; not specified in text. Page 83 O tenuous connection to the main portion of the larva's body. Moreover, the surface of the larva's body became covered with very fine, spine-like structures, and depressions recognizable as the beginnings of bothria developed at one end. From this part of the body toward the interior cari be seen a radially disposed, elon- gated group of cells. After four weeks had passed, the spherical body that possessed the hooks became detached from the constricted area, and eventually it shriveled up, setting the hooks free. These hooks could be observed remaining within the body of the Cyclops for a long time afterwards. The main part of the larva's body had reached a maximum length of 0.5 to 0.6 mm, and the calcareous bodies numbered from 6 to as many as 22 or even more. Subsequently the tapeworm

continued to develop and remained parasitic on the Cyclops for a lengthy period,

although no further morphological changes appeared to take place. • The above observations pertained to the extent of growth of D. latus larvae within the bodies of Cyclops sternuus specimens. However, in addition to these types of experiments, other tests, too, were performed involving six-hooked larvae

being placed together with Cyclops, as not only C. sternuus but several other

species of Cyclops, too, were put together with other aquatic animals and the larvae. When specimens were prepared an July 31, 1925, it was discovered that

not only Cyclops sternuus but also Cyclops leuckartii Sars had been infected with larval tapeworms. That is, numerous larvae were observed within the body cavities of the C. leuckartii specimens. One of these types of larvae had an elongated ellipsoidal shape and already exhibited rudimentary bothria, while at its other end was appended a spherical body that possessed hooks, this body being attached by a fine, narrow stalk. Also parasitizing these specimens were a number of larvae that had not yet assumed an elongated ellipsoidal shape by becoming • constricted at one end; hooks appeared in this region, and no calcareous bodies • Page 84 at all could be observed in these larvae. However, these larvae perished while

being transported from the research site, so that the experiments ended without having an opportunity to feed them to fish. A subsequent follow-up study that had been planned could not be carried out because all of the dogs that had been infected with cultivated tapeworms died.

Chapter 4. Experiments an the Migration of D. latus Larvae From Their First to Their Second Intermediate Host Section 1. Experimental Materials and Methods

Larval tapeworms that grew within the bodies of the Cyclops spec- /p. 54 imens discussed in the previous chapter were used by the author in subsequent experiments designed to study how the parasites migrate to their second inter- mediate host. These later experiments were the ones that the author concentrated • most of his energies an, as they formed the central focus of this research. The aspect of the study that the author found most difficult was the problem of obtaining fishes that could be a second intermediate host of D. latus but which were completely devoid of natural infection by the plerocercoids of this tapeworm. This [freedom from prior infection] was at the same time the most important point that had to be ensured in the experiments. Since salmons and trouts in general are extremely sensitive to the conditions of their environment, and since, more- over, they are fishes that live in clear, cold water, several full years of

painstaking work are required to artificially hatch and raise them. With this purpose in mind, the author on two occasions, once in 1922 and again in 1923, attempted to hatch and rear fishes, using fish eggs that had been collected on expeditions he made to the upper reaches of the Maze-gawa and the upper reaches of the Nagara-gawa (at Hachiman in Gujo District, Gifu Prefecture). Masou salmon • eggs were taken from the former river and grass carp eggs from the 1att6r. The Page 85 gl› author waited until the eggs had reached the eyed period, at which time they were placed in an egg transporter and moved to his laboratory. The eggs were then put in the laboratory's experimental pond, and an attempt was made to hatch them and raise any resulting fish, with a constant flow of municipal water being maintained in the pond during this period. However, in the end both of these attempts to artificially hatch fish ended in total failure, as all of the specimens perished on account of marked changes that took place in the temperature of the municipal water around the time the yolk sacs completely disappeared, problems connected with feeding the fish, etc. At this point the author felt as if he had no alternative but to abandon the planned experiments. Nevertheless, in the fall of 1924, a fish breeding experiment station was established on the outskirts of Ogaki City, and permission was given to the author to set up an experimental pond within the facility. His spirits thus buoyed, the author decided to resume his research. Excessive fluctuations of the water tempera- ture could be minimized and clear, cool water could be provided at this facility,

for [the water was supplied from] a number of underground pits that had been dug out on the outskirts of Ogaki to allow [spring] water to gush up. This was a very suitable site to establish a pond for culturing salmon and trout. In the experimental pond set up here the author artificially hatched and reared grass carp from the Nagara-gawa, masou salmon from the Maze-gawa (the upper course of the Kiso-gawa), and rainbow trout from the Ibi-gawa, and then used these fish in his research. The approach employed in hatching the fish was as follows. First the eggs were collected and induced to become fertilized, and then they were incubated* in mountain streams in their native areas; that is, Naratani in Ono District of Gifu Prefecture in the case of the masou salmon, Hachiman in

*Translator's note: Inference. The Japanese word used here normally means uhatchedu. lie Page 86 Gujo District in the case of the grass carp, and the upper reaches of the Ibi-gawa In the case of the rainbow trout. After these [eggs] had reached the eyed stage, they were brought to the experimental pond. The water gushing into the bottom of the pond was made to absorb additional oxygen by bringing it up into the air once. This gushing water was then kept flowing through the experimental pond,

and [the fish] were artificially reared using a mixture of silkworm pupae and bean scraps. Consequently, there is ample support for the observation that these fishes were completely free of natural infections by Dibothriocephalus latus or other tapeworms, etc. When these fishes were employed in the experimental inges-

tion tests, the material being fed them was taken up with a pipette and passed through the fish's oral cavity and deposited directly into its stomach. Never- theless, the author experienced nothing but difficulty in trying to obtain positive gl, results. The material fed to the fish could easily leak back out through the gills, and on many occasions the fish would vomit out the food they had received as soon as they were returned to the water. Moreover, when fishes belonging to some of the more sensitive genera are reared artificially, they will refuse to take food for days at a stretch; these types of fish died during the experiments, as did other fishes that were very sensitive to water temperature. Yet, despite the myriad troubles, the author finally managed to achieve a certain measure of success. The author will now attempt to describe these results and present them for the reader's consideration. Section 2. Experimental Results /1) . 55 Experiment 1 November 8, 1923 Larval tapemmrms that had parasitized and developed within Cyclops were fed to two carp. Approximately 20 of these Cyclops were fed to each of these 111, fish. When necropsies were performed on the carp on January 20, 1924, no plero- Page 87 cercoids were observed infecting their alimentary canals, viscera, or muscles.

Experiment 2 June 14, 1924 Cyclops that were infected by larval tapeworms were fed to five grass carp that had been hatched from eggs collected in September, 1923. Three of these five fish died during the experiment. When the remaining two grass carp were necropsied an July 8, it could plainly be seen by the naked eye that a larval tapeworm had parasitized the muscles in the neck region of one of these fish, and that muscles near its head had become infected with a large, white dot-like substance that was about the size of the head of a sewing needle. Histological examination of [a similar dot-like substance] in the second fish confirmed that it was structurally identical in every respect to the plerocercoids of D. latus, so that both of these grass carp were confirmed to have become infected with • this tapeworm's plerocercoids in their very youngest form. Furthermore, marked cell infiltration was observed surrounding the larval tapeworms in the muscles that they had parasitized.

Experiment 3 July 8, 1924 Three juvenile grass carp (ones that had hatched in September, 1923) were fed Cyclops that bore D. latus larvae. All of these fish, however, died during the experiment, before the intended number of days had passed. The stomach contents of the grass carp that died on July 9 were examined, and only a larval

tapeworm that had left the body of the Cyclops could be detected; in the end there was no evidence that the fish had becone parasitized by a plerocercoid.

Experiment 4 August 30, 1924 Six-hooked larvae obtained by cultivation were allowed to enter the bodies of Cyclops and grow there to a certain stage of development. These [Cyclops] --- were then fed to three rainbow trout that had hatched in April, 1923. The first Page 88

• of these trout died on 3, September and the second died on September 7. When their stomach contents were investigated on necropsy, no larval tapeworms were discovered, and no signs of parasitism in the stomach wall or muscles could be observed by the naked eye. Only one of these rainbow trout managed to survive, and, after it had passed through the critical days following the end of the feed- ing experiment, it ate its [normal] food and continued to live for a long time. Finally, on October 19, this fish was necropsied and found to have been infected with three larval tapeworms. When one of these larvae was taken up in salt water and examined, it was found to have a pair of dorsoventral bothria in its head region, and it also demonstrated expanding-and-contracting motions as well as

vermicular motions. This larva showed the saine features as the ones the author discovered in masou salmon from the Jintsu-gawa. The author took one of these larvae - a specimen that was 10 mm long and 1 mm wide when contracted - and fed it experimentally to a cat. Examination of the stools of this cat on November 7 confirmed the presence of the eggs of Dibothriocephalus latus, [indicating] that the cat had become parasitized by an adult tapeworm. A histological exam- ination was made of another of the larval tapeworms that had infected the rainbow trout, and it was found that the general structure of this larva did not differ in any respect from that of the plerocercoids encountered in naturally infected [fish]. (See the appended plates.) The features of this larva agreed with those of the immature form of D. latus that infected masou salmon from the Jintsu-gawa. If we compare this larva with the one found in the grass carp described above, we can note that it showed greater growth in the muscles [of the fish], and also that numerous calcareous bodies had formed.

Experiment 5 September 16, 1924 Three rainbow trout that had hatched in April, 1923, were fed Cyclops that • Page 89 were infected with D. latus tapeworms. One of these fishes died on September 19, and no larval tapeworms, etc., were found among its stomach contents when the fish was necropsied. When the mucous membrane [of the stomach] was cleared away and a further examination made, a larval tapeworm was discovered. However, no other tapeworm larvae could be found anywhere else. The second of the trout died on October 19 and the third on December 25, but no larval tapeworms could be detected with the naked eye on necropsy of either fish. (Although both of these fishes had been fixed in formalin prior to the examination, detailed results were not obtained for them.)

Experiment 6 December 25, 1924 The Cyclops used in this ingestion experiment were ones which had been penetrated and infected by numerous six-hooked larvae that were small and rather • poorly developed. These Cyclops were ingested by three fishes of a mixed species (grass carp and masou salmon) that had hatched in September, 1923. The first of these fishes died on December 26, [1924], and necropsy disclosed that a larval tapeworm that had left a Cyclops had moved into the mucous membrane lining the stomach of the fish. The second of these fishes died on December 30, but no tapeworm larvae were observed on necropsy. The third fish died an June 29, 1925. When a necropsy was performed on this latter fish, the author found it to be infected with two plerocercoids that had a morphological structure absolutely identical to that he had previously observed in masou salmon from the Jintsu-gawa.

Experiment 7 June 25, 1925 /p. 56 Larval tapeworms that had grown to a size of about 0.5 mm in the bodies of Cyclops were fed to one masou salmon and three grass carp that had been artifi- cially hatched. The masou salmon perished on July 5 and was necropsied. This • examination revealed the presence of [a] small dot-like body about the size of Page 90 the head of a sewing needle near the area of the stomach wall where [material] passes into the intestines. Under the microscope it was confirmed that this was an extremely immature plerocercoid. The second and third fishes - grass carp - died in the last week or so of July and were fixed in formalin prior to being examined. Although a loss of [staining] coloration obscured the details in these specimens, no larval tapeworms could be detected with the unaided eye when they were finally inspected. The last of the fish, also a grass carp, was necropsied on August 3 and was found to be infected with extremely immature plerocercoids. These plerocercoids were discovered outside of the intestinal serous membrane and in the muscles of the fish. When they were fed experimentally

to a dog, no adult tapeworms could be obtained. It is suspected, however, that this failure can be accounted for by the fact that these plerocercoids were very Ili immaturely developed and, as a result, were not robust enough to remain viable and parasitize the dog.

Section 3. Summary of Experiments /1) . 57 In the seven experiments described above, the author fed to various fishes larval tapeworms that had been allowed to parasitize and grow to some extent within the bodies of Cyclops. The fishes used in this study were carp that were free of natural infections and several artificially hatched fishes, i.e., one masou salmon, six rainbow trout, 11 grass carp, and three of a mixed species (masou salmon and grass carp). Two of the grass carp, two of the fishes of the mixed (grass carp and masou salmon) species, and one of the rainbow trout were found to have become obviously infected with larvae that had grown to the plero- cercoid stage. In addition, larvae that had penetrated into the stomach wall were also detected in some of the fishes studied. Plerocercoids that had thus been able to infect fishes were subsequently fed to a dog and a cat, and it was • Page 91 found that the plerocercoid ingested by the cat was able to develop into an adult Dibothriocephalus latus tapeworm. The author considers this to be a case where a D.latus tapeworm was brought through its entire growth cycle experimentally. Moreover, when the stomach contents of the fishes were examined about 24 hours after they had been fed, larval tapeworms that had freed themselves from

the Cyclops were detected. Tapeworm larvae were also discovered when the mucous membrane lining their stomachs was cleared away. These findings appear to indicate that the tapeworm larvae leave the first intermediate host when they are in the fish's stomach and then penetrate [into the fish] through its stomach wall. How- ever, since only a small number of cases could be investigated in this study on account of the difficulty of obtaining test materials, it would be premature to immediately state, on the basis of these results alone, that the larvae only penetrate through the stomach wall, for the possibility remains that some larvae penetrate through the intestinal walls. Furthermore, as was seen in two of the rainbow trout studied, larval tapeworms (plerocercoids) can also develop to some extent while they are in the stomach wall and in the serous membrane lining the stomach. This discovery suggests the possibility that tapeworm larvae may migrate to the muscles after they have remained for a fairly long time in the stomach wall.

When histological examinations were made of the larval tapeworms /p. 58 that had infected these artificially produced salmonids, they were found to be immature forms that were not significantly different in any respect, at least histologically, from the larvae seen in natural infections. Few calcareous bodies were observed on these larvae, and their cuticles and muscle layers were only

weRkly developed. Strong cell infiltration was observed in the vicinity of.the 411 larval tapeworms in the stomach walls and muscles that they had parasitized. • Page 92 Furthermore, in some cases similar cell infiltrations were discovered in areas believed to be the paths of their migration.

Chapter 5. Summary of Part IV (With Special Reference to the Life History of D. latus in Japan) Reviewing the results of the experiments discussed in Chapters 2 through 5 above, the author believes he has confirmed that the principal first intermediate

host of D. latus in Japan is Cyclops sternuus Fischer, and that Cyclops leuckartii can also serve as a first intermediate host for this tapeworm.

D. latus eggs were found to develop most rapidly at a temperature between 28-30 ° C, but they also were able to grow at temperatures as low as 22 ° C. There- fore, we can state that these eggs stop developing during the cold winter, but when warm weather arrives in the spring the egg cells begin to divide. These egg cells use the yolk sac for nourishment as they divide and grow, and they become distinguishable as forming a covering type of cell group and as a cell aggregation that gives rise to the tapeworm's body. The latter cells further divide to form a rounded cell aggregation that is the primitively developed body of the larva. This primitive body is then enveloped by the group of cells that serves as a covering. Cilia also develop on the surface [of the covering layer], and and six hooks form within the body as it grows into a hexacanth larva. This larva will eventually go out into the water and swim vigorously.

In view of the above results, the author conducted several experiments to study the interrelationships between these six-hooked larvae and some aquatic animals, and then he was able to do a follow-up study on the extent of growth

that these six-hooked larvae achieve inside the body of Cyclops sternuus. In addition [to C. sternuus], the author observed that, on a few occasions, this 41, tapeworm penetrated into the body of Cyclops leuckartii and developed tliere. • Page 93 However, even if these tapeworms were able to enter the bodies of the other aquatic animals, they were not able to grow inside them. That is, larvae that were placed in the stomachs of the Cyclops referred to above bore through the stomach wall and penetrated into the body cavity of the copepod, where the primitively developed body of the larva then assumed an elongated ellipsoidal shape before a spherical body that gathered the hooks together was formed at one end. The spherical body that developed at the area with the hooks eventually constricted [at one end] and separated from the main part of the body, and then bothria were formed on the main part of the body. Subsequently the Cyclops that had become infected

with these larvae were fed by the author to artificially hatched fishes - that is, to fishes that were undoubtedly free from tapeworm infections. These test fishes comprised one juvenile masou salmon, six rainbow trout, 11 grass carp, • and three fishes of a mixed species (masou salmon and grass carp). In these experiments it was observed that the larvae had clearly developed to the pler- ocercoid stage in two of the grass carp, two of the masou salmon (including one that was actually a mixed species with grass carp), and one of the rainbow trout. In some of the other cases, too, larval penetration into the wall of the salmonid's stomach was dbserved, and there were also instances where the larva showed slight growth within the stomach wall. When the plerocercoid that had infected the masou salmon was fed to a cat in a follow-up study, a complete, adult tapeworm was obtained. The larval tapeworms that were obtained from the experimentally infected masou salmon and other fishes were confirmed to be the same, both morphologically and biologically, as the larval tapeworms that para-

sitize masou salmon under natural conditions. AD. 59 However, other experiments that have been performed on this topic would • seem to lend no support to these findings, as nothing but negative results have Page 94 been obtained when eggs or six-hooked larvae [of D. latus] have been fed to masou salmon, etc. If we look [more closely] at the results of the present study, however, we see that it is an indispensable condition for successful parasiti-

zation by D. latus that a first and second intermediate host be present, and it also seems evident that the first intermediate hosts of this tapeworm are Cyclops crustaceans. In the preceding parts of this study the author has tried to describe, how-

ever poorly, his own attempts to unravel the life history of the Dibothriocephalus

latus tapeworms found in Japan. The author's own research results provide the

basis of this study, but reference has also been made to experimental results published by his forerunner in this field, Dr. Ijima, and by Janicki and Rosen. Although human beings are the most common definitive host of this tapeworm, dogs, cats, and bears, too, are frequently infected by it, too. Furthermore, the author confirmed cases where each of these animals had been naturally infected, and also carried out experiments in which a human being, dogs and cats ingested plerocercoids and became parasitized by fully grown adult tapeworms. No signif- icant differences could be seen in the extent of development shown by these tape- worms in these hosts. Tapeworms that are found in human beings and in bears are often relatively large in size. This is probably explained by the fact that the site that they parasitize in these instances - the intestinal canal - is itself large, and the fact that the tapeworms are able to infect these hosts for a longer period of time than is the case with cats and dogs. This tapeworm's life-span appears to be briefest in cats, and no cases have been Observed where a dog has remained infected for over a year. D. latus grows rapidly within the body of its host, as average daily increases of 1.8 to 11.5 mm in length and anywhere between 8 and 71 proglottids were observed in this study. • Page 95 Dr. Ijima reported that the second intermediate host of the D. latus tapeworms

in Japan is the salmon Oncorhynchus perryi. According to the author's studies, the most common host of this parasite in Japan is indeed a salmon, but its sci- entific name is Oncorhynchus masou Blebord. It should be pointed out here that the difference between the scientific names used by Dr. Ijima and the author comes down to the fact that the fish usually referred to [in Japanese] simply as nmasull (i.e., salmon) is now known scientifically as Oncorhynchus masou, whereas the fish designated O. perryi should now be called Hitomi masun or Salmo perryi, according to Dr. Fujita's theory. However, based on the description he provided,

the fish Dr. Ijima was referring to should more appropriately be regarded as masun not Hitomi masun.

The author found in his investigations that 3.29% of the masou salmon sampled from the Jintsu-gawa, 20% of the masou salmon from the Shirakawa River, and 1.89% of the masou salmon from the Kiso-gawa were infected with plerocercoids, and that the infection rate was higher in the salmon from areas near the coast of the Sea of Japan than in those from sites near the Pacific Coast. Fishes other than masou salmon were also investigated. Since the author was able to experimentally infect grass carp (a variety of masou salmon) and rainbow trout (Salmo iridius) with plerocercoids, it must be assumed that these fishes, too, sometimes play

the role of second intermediate host for this tapeworm in nature. However, since grass carp and rainbow trout are not very numerous these days in waters near the coast of the Sea of Japan, it does not seem likely that they occupy a very important position in the infection route of D. latus. Moreover, although chum

salmon and other salmonid fishes probably can also serve as second intermediate hosts for this parasite, this has not yet been verified in the author's studies. • According to the results of the author's research, the first /p. 60 Page 96

intermediate host of D. latus here in Japan is Cyclops. Since the larvae of this tapeworm are able to infect and reach full development in Cyclops sternuus, the author believes that C. sternuus is the primary first intermediate host of D. latue in Japan. Although there are also other species of Cyclops in Japan - e.g., C. serrulatus, C. leuckartii, C. magnoctavus, C. signatus, C. flexopedum,

C. soli, and C. phaleratus var. japonica, among others - so far the author has only encountered one other case where a larva of this tapeworm developed to some extent within the body of a Cyclops; that was a C. leuckartii specimen. in every other instance, negative results have been obtained in attempts to infect the

Cyclops with these larvae. Therefore, it is the author's view that C. leuckartii can sometimes be the first intermediate host of D. latus. Other work has also been done to investigate whether Cyclops is a first intermediate host of D. latus. Janicki and Rosen allowed six-hooked larvae to grow within the bodies of Cyclops, and then fed these experimentally to Esox lucius. These researchers verified that the larvae penetrated into the stomach

walls of these fishes, and then supposed that they migrated into the fishes' muscles and became plerocercoids. The present author's experiments employed

Cyclops and masou salmon, rainbow trout, and grass carp that had been artificially hatched and thus had not been naturally infected by these larval tapeworms. By

means of these studies the interrelationships among [the larvae, Cyclops and fishes] could be further elucidated. That is, by cultivating D. latus eggs that had been obtained through the experimental feeding of plerocercoids from naturally spawned masou salmon, the author grew six-hooked larvae, which were then placed together with artificially hatched Cyclops. A follow-up study showed that these larvae developed to a certain extent within the bodies of these crustaceans. • When infected Cyclops were later provided orally to artificially hatched masou • Page 97 salmon, grass carp and rainbow trout, it was established that the larvae could grow into fully developed [plerocercoids] within the muscles of the fishes, and when one of these [plerocercoids] was subsequently eaten by a cat a D. latus tapeworm was obtained. The author thus believes he has now demonstrated exper- imentally the entire life history of Dibothriocephalus latus, and that he has been able to determine the first intermediate hosts of this tapeworm in Japan. His work forces a reassessment of certain aspects of the views propounded by Janicki and Rosen on the first intermediate hosts of D. latus, but also provides additional confirmation for other aspects, and thus serves to supplement our knowledge of this tapeworm's growth cycle.

Overall Summary

The following is a broad summary of the material presented above in the four major parts of this publication. (1) Although infections with Dibothriocephalus latus are encountered here and there throughout Japan, they appear to occur extensively in the Hokuriku region in particular. Accordingly, the author conducted a statistical study in

Gifu Prefecture over a four-year period and found that victims of D. latus para- sitization were especially numerous in the drainage areas of the Jintsu-gawa and other rivers which empty into the Sea of Japan, whereas infection with this tapeworm is rather rare in the basin of the Kiso-gawa and other rivers that flow into the Pacific Ocean. When this relationship was further investigated by taking into account the distribution of fishes in these areas, it was observed that there were many victims of D. latus infection in regions where large numbers of masou salmon were caught.

(2) The relationships between D. latus infection and sex, occupation and age were also investigated. The relationships that were noted were believed Page 98 to be connected with the issue of whether or not fish, the intermediate host of this tapeworm, was being eaten raw. Age itself did not appear to be a factor.

(3) According to the results of the author's studies, the most /p. 61 important of the second intermediate hosts of D. latus in Japan is the masou salmon Oncorhynchus masou Blebord. Of 85 masou salmon from the Jintsu-gawa that the author examined, 28 (32.94%) had been infected by the plerocercoid of this tapeworm, and one of the five masou salmon (20%) from the Shirakawa River was similarly parasitized. On the other hand, only one of the 53 masou salmon (1.89%) from the Kiso-gawa was observed to be infected by its plerocercoid. Five masou salmon from the Tone-gawa and five coho salmon from Hokkaido were also examined, but no D. latus plerocercoids could be detected in any of them. (4) Fishes other than masou salmon were also investigated. These included • the grass carp, chum salmon, sweet smelt (ayu), coho salmon, char, chub, the carp Cyprinus carpio, masu salmon, bullhead, dace, greenling, loach, the carp Zacco platypus, etc. None of these fishes, however, were observed to be infected with plerocercoids. (5) As for the site within the body of the masou salmon that is parasitized by the D. latus plerocercoid, infection was detected most often in the dorsal muscles, the dorsal muscles of the abdominal wall, and other muscles of the

abdominal wall. Next most frequently infected, in order, were the muscles in the thoracic, neck and caudal regions, then the viscera, and finally the abdominal cavity, where the parasite was found free. Although in most cases the [plerocer- cold] was not encysted, some instances of cyst formation were observed. However, these cases only accounted for 10.1% of the all of the plerocercoids found. (6) The plerocercoids of D. latus exhibit fairly strong resistance, as they • were able to survive for several days in tap water and in salt water before they • Page 99 finally died, gradually becoming softer and disintegrating from their posterior end onward. Moreover, the plerocercoids lived for three or more days in [fish] flesh that was rotten, pickled in brine or packed in ice, and they did not succumb, either, when immersed for 10 minutes in soy sauce, sanbaizu, etc. It was observed, however, that larvae that had been placed in boiling [water] for five minutes or had been smoked for 10 minutes died. (7) When plerocercoids were ingested for experimental purposes by a human being, dogs and cats, it was found that the larvae grew into adult tapeworms. However, adult tapeworms did not develop when monkeys, guinea pigs, white rats,

chickens, etc., were used in ingestion tests. That is, man, dogs and cats are definitive hosts of D. latus. Human beings are considered to be the most common final host of this tapeworm in nature, and cases of dogs being infected have also been observed. The author has confirmed a case moreover, where a bear was naturally parasitized by D. latus. Therefore, human beings, dogs, cats and bears are second intermediate* hosts of this parasite. (8) The shortest number of days that elapsed from the time a plerocercoid of D. latus was eaten by a definitive host until the time it developed into an adult tapeworm - inotherwords, the number of days that passed until eggs were

shed - was found to be 14. The tapeworms grew by an average of 1.8 to 11.5 an per day, with the daily increase in the number of proglottids being anywhere between 8 and 71, usually falling within the 40-50 range. The tapeworm lives for a relatively short time within the body of its final host. This parasite does not stay in the human body for more than a couple of years, whereas in dogs it is eliminated within a year and in cats in an even shorter time. As a result, the D. latus tapeworms found in cats are small, and those occurring in dogs are

• *Translator's note: Sic. Evidently the author meant definitive hosts. • Page 100

somewhat smaller than those infecting human beings and bears. However, as far

as the state of the tapeworm at its different stages of growth are concerned,

no major differences are observed between the D. latus worms found in man and

those parasitizing dogs and cats. /p. 62

(9) The eggs of this tapeworm were found to develop at room temperature

between May and September, and their growth was especially rapid when they were

placed in an incubator set at 28-30 ° C. When the eggs developed at room temper-

ature, two to three weeks were required for six-hooked larvae ("oncospheres")

to be formed, whereas six-hooked larvae appeared in about two weeks when the

eggs were in an incubator. These hexacanth larvae gradually matured, and in

the end broke through their egg shells and emerged into the water, where they

began to swim vigorously with the aid of long cilia.

(10) The first intermediate host of D. latus is the crustacean Cyclops.

That is, when the author placed six-hooked larvae within the same habitat as

Cyclops that had been artificially hatched, and were thus free of suspicion of

having been naturally infected, the six-hooked larvae entered the bodies of the

Cyclops, penetrating the walls of their alimentary canal and entering their

abdominal cavity. They then assumed an elongated ellipsoidal form, with the

hooked end becoming constricted and falling off, and numerous calcareous bodies

formed within the body. Rudimentary bothria also began to develop at this stage.

(11) The larval tapeworms ("procercoids") that developed within the bodies

of the Cyclops referred to above were ingested by fishes that had been artificially

hatched and had thus not been naturally infected by the tapeworm. , These fishes

included the masou salmon*Oncorhynchus masou, the grass carp (a variety of masou --- • salmon), and the rainbow trout Salmo iridius. • These procercoids penetrated the stomach walls of the fishes and entered their muscles, where they developed into • Page 101

plerocercoids. When [one of] the resulting plerocercoids was ingested by [a] cat, an adult tapeworm developed within the cat.

(12) According to the author's research results, Cyclops sternuus plays

the most important role as a first intermediate host of D. latus in Japan. Cyclops leuckartii, too, also can be a first intermediate host of this tapeworm. Although

other species of Cyclops are also found in Japan - e.g., C. serrulatus, C. soli, C. signatus, C. flexopedum, C. phaleratus var. Japanicus, C. magnoctavus, etc.

- none of these has yet been demonstrated to be a first intermediate host of D.

latus. (13) As has been discussed above, the only species that has so far been

confirmed to be a second intermediate host of D. latus under natural conditions

in Japan is the masou salmon Oncorhynchus masou. Nevertheless, since the author has also been able to experimentally infect grass carp and rainbow trout with its plerocercoids, it seems reasonable that these fishes, too, may well serve as

second intermediate hosts of D. latus.

• (Translator's note: The author's acknowledgements have not been translated.) • Page 102

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Fauna Arctic* von Fritz AbramOwski: Zur Frage Ube, den•mutmasslicheri Zusammenhang zwischen der Erkrankung an Bandwurm, speziell Bothrincephalus Lotus und derjenigen an Lungentuberculose. Fortschr. d. Med. 19o9. sz.) Krebbe: Das Vorkommen der Teniaarten beina Menschen in Danninark. Nardisk. medicinsk Arkiv, 1396. (Ref. in Lubarsch.Gate. rtates Ergebnisse VU. agar). • 11) Slavers, • R.: Zur Kentnis der Verbreitung von Darnaparasiten in >inland. Festschri(t rdr Pahuen, No. In. 19o$. (Ref. in Cent. f. Bad. etc. Mit. I. Bd. 38, 1906). le.) Babes: Lieber den Dibothriocephalus talus und die Boshriocephalen•Anamie in Iturnanien. Virchowts Archly. 141. 1189S. 85.) Max Koch: 1101tere tkrische Parasiten. Lubarschestertagis Ergebnisse, Bd. XIV. 1919. s6.) Kaesevittrm. P. und Steinbruok: Tierische Parasiten ais Krankheitserreger 13ei Ilaustieren. Lubarsch.Ostertag/s Ergebnisse, 'Bd. VIII. sgoz. 17.) Braun, M.: Zur Frage d. Zwischenwirt. von Bothriocephalus latue. Zool. Ant. IV, V, VI. 188z-1833. s8.) Braun, M.: Bothriocephalus latus und seine Ilerkunli. Virchow/s Archiy, LXXXVIII, :882. XCII. 1933. 19.) Kuachenmeister, F.: Wie steckt sich d. Mensch mit Both. latus an ? lied. Id. Wochschr. XXII. 1835.-Die Finie d. Bothr. u. seine Uebertr. a. d. Menschen.-Weit. llestSt. meiner Behaupturig. die Finne des Ilechtes hat nichts mit fouir. latus ma tun. Deutsche aned..Wochschr. s886. 2o.) Braun, N.: Salm oder Hecht ? Ben 1. Wochschr. XXII. s885.-Uber den Zwischenwirt des breiten Bandwurms, eine Entgegnung an KUchenincister. 1886. Botlariocepltalus.Finnen un es St. Petersb. Fisclamarkte. St. Petersb. med. Woclaschr. XVII. Nr. Z. 189,..-Ileintinthorogischen Notizen. I. Centr. f. Bact. etc. XIV 1393. 2s.) Cried, B. u. Ferrara: 7 hrlocephalusfrage. Deutsche me& Wochschr. 1886. 22.) Leuckart, R.: Zut Ilathrinceplaalusfrage. Cent. f. Bakt. etc. I. 1887. 23.) PerOna, E.: II Bothriocephalus latus in Lombard. Rend. R. lstit. I.omb. (2) XIX..-Sulla quest. d. »attn. latus Gazz. med. ital. lpmb. 1336. (Referatr. 0"). 24.) Bevil.: Sur la pre& du . 11othriocephalus de Illumine. C. R. cc. sc. I.VII, 139o. 25.) Beneden, E. van: run la pres. en Bag, du Bothriocephalus latus. Ilull. Ac. Roy. %lg. (3). XI, 1889. 26.) Berkeley, W.. N.: A case Of »attar. with rem. on the nee. of Bothr. in America..Med. MC. .N. York. !XIII, 1903. 27.) Clurca, Jean: Itothriocephalua.Finnen in IlecIsten und 13arschen aus den Teichen der Donaugegend. Zeitschr. f. Fleisch. u. blitchhyg. Jg. at. 19: t. a8.) Grassi, B. u. G. Rovelli: Ilmulwuran.Entwieklung. Cent. f. Baca. etc. Ill, Tb. Pe The Eggs of Diphylobothrium laturn. JI. Amer. med. ass. LXXIII, 1919. 30.) Nickerson, W. S.: - _ 29.) Magath, The broad tapeworm in Minesata. JI. Amer. sued. ass. !XXIV, 1919. 31.) Riley, W. A.: The bond tapeworm, Dib nhr. latus in Minesota. JI. amer, med. ass. I.XXIII, 32.) Riley, W. A. The longevity of the rash tapeworm of man, Dibothr. latus. JI. paras. V, s919. 33) Singer, J. J.: A case of Bothr. lattis infection. JI. Amer. med. ass. I.XVI, 19s6. U.) Zschokke, Fe Der lkohr. lattis in (;enf. Cent. f. Bret. etc. I, I387. 35.) Zschokke, Weft= Zwischenwirt der Bothr. talus. Ibid. IV. u. Vil. 1337489o. 36.) Schor, Me Contrib. a Vet. du Bothr. latus dans le canton de aud. These. Lausanne. (Cent. f. Bsct. etc. I. abt. Ref. XXXIII, 19)3). 37.) Killich, R.: Esperimentelle Unetrsuchungen durch Gefrieren, zeitsdm f. Fleischlayg. 1923. 3s.) Kethariner, L. Vas Fitanigwerden der Sasswasserfische durch Uebertragung der aus den Elena des breiten Ilandwunn (Dibothr. lamas). ausgeschlupften 1.arveti und Ober die angeblicle grass= Ilitufigkeit der Art in der Westschweit. bliinchen med. Wochschr. *918. 39.) Galli-Valerio: Bothriocephalus talus Lei IIund und Katre. Cent. f. Bad. etc. XXXV, son. and Para. 4'1.) Sbno Von Ritz: Dibothriacephalus latus int Mande. Cent, f. Baeg. etc, Aht. I. ore Bd. XXXV1. 41.) Underhill, B. M.: Parasites Veber Bothriocephalen. sitosis of the Domestic Animals. 2920 42.) Wee .1 gretta Ai "Tit Ebb SeBiee• /112561e WI MN I-Z:1f. 43.) ZsohOkke, S.: larven in Trutta salar. Cent. t Beet. etc. VII. 8891. 44) Mueller, Max: Zuni Nachweis der Lebensfithigkeit der Fannen in Gallekochsalzlbsungen nach Franke. (Ref. in. Cent.. f. But. etc. Bd. 75). 45.) Authur Bosttoher: Studien Ober den Bau des Bathr. latus. Virchowts Archiy. XXX. *864. 46.) Mosier, Fr.: tlebes LebenscLauer und Renitenz des Bothr. latus. Virchowts Archie. LVU, 1873. 47.) Georg Walter: Beitrage sur mikroskopi- schen• Anatomie der Nernstoden. VirchowPs Archie. XXXIV. 8862. 48.) Otto Riegel': Blutkrankheiten und Blutdiagnostik. 1933: • Page 103

49.).Sohaumann, ()aslant Welche Rolle spielt das konstitutinnelle Moment in der Pathogenzse der Dothrincephalusanamie ? Deutsch. med. Wochschr. : in. So.) Braun Seifert: Die Tierischen Pamsiten des Menschen. .tgas. St.) Kothm, A.: Veber Sparganum liaillkti R( tz und den zugehisrigen geschre- \ . Bothr. chtreifer Bandwurm , Dtbothr. Relined Ritz. Cent. f. »act etc. Bd. go. toas. 52-) Esohr6oht D. F.: Anat.•phys. Untersuchungen liber die N. Act. .Ac. Canes. nt. curio% XIX. Stipp!. II. tSt4. (Rita u 40. 53.) Bah4u1ndand, Embryon. •Entwicklung d. Ikuhrlocephalus. Jenaische Zeitschr. >lawny. XIX. res. $4.) knoch, J.: Vorlaufige Mitttsellungen *bet den Ituthr. lam% dia Entwickelung &neaten, die Wanderung und endlicli Uebertragung seines EmbryoPs in den Menschen. Vkchotes Archie. XXIV. diet*. SI.) 'Untold. O. V.: Uttar den Prod's* der Ilullnem branenbildung In der Entwkithang des Ikuhrloosphalenekts. Lii. Ana, Dd. 34. spy. (Ceti. I, Deg. etc Abt, II. Dd. 464 ton> ye.) Jenlokl, 0.1

lixperimentelle Untemuchungen ear Entwklilaag enn Ihbultr. late*. I. Usher negative Versuche, binge Forellrn, litchi. taut lunar duseLt. . mil Flimtuerembryonen su Widen*. Cent. f. Rea. me. AM. I. Org. hit. eel. $7.) "I* ontli*Ingift • **ale / 'F. Hiapp., /11-11/111 1.Flat.*Zte7:41. Janlokl. C. et Ram, F•' la cycle liedutlf dim 1)itzuhr4orephalus Imes I.. hull, $ ic. Neuehitel im. wat, XI.11. tut'. 39.1 Janlokl. 0 it Rom. F.: Me Enterkithingszycles eon Ditiahr. Imes I. Ownwpweireseld. V. Ikherelger Aerate, soy. N.b, 4 , (r1) Nybelln. 7.ur Erage der Emwickluognewchichw enter Dothriocephalklen.. Gâtebrege 141. Vetenstiouch Viltrrliettunth„ Ilende, 4, Vojta, Ik1 XIX, y. ■ (kgebueg •91D. (Ref. in Cent. f. Bach est Kat M. 68. $919. 6i.) Jattlokl, CIA Neue litudien Ober Posten bryonale Enterkklung und wirtsweckel bel Dothriocephalen. II. 1):4 Gattung IAgula. Owresperulcnabt. I. Schweizer Aerate. two. (Ref. in Cent. t. Wet. etc. It. Abt. L ltd. (..9. tnao).

62.) Nybalin. O.: Entwickhnigsgeschichte von Schistocephalus solidus. (C F, Muller) Cent. f. Bad. etc, Abt. I. Org. Bd. S3. $eg.

63-) °Imam, T.: An experimental Study of the lifehistory of Sparganum mansoni. Kitasato. Archie of Eexp. med. vol. III, No. 3. tot% 64.) Karl Camillo Solmelder: Cestoden. • Lehrbuch der vergleichenden histologie. 65.) Butter Bull. U. S. Eish Commission for a9os. 66.) will's, H. Mot Returus from the experiments on the marking of young chinock salmo on the Columbia River. U. S. Bar. Fish. Econ. Circ..No. 45. (re(.w. 67.) 11144: tteint%Ifithi: OtbOBItIt3443t. 68-) Moe: Inlitei.lcIE15141. 69.) E1341: n 4:fte. meter:. 7..) a*ok*Ateeli. *elm- 71). 73.) +Me 114:11U1 tbibeSte aotit. llIt/iP1 -1-1011. 73.) fiat: AMCOR. 74.) ari: Min »111).1;e* setnIgliegktbek (Plerocercoid) itteeiretwer..1-xente. Ic-.E .1--#1. 75.) an anelzuezt) wiz z-migie. dowete gi-zige.**EtEitt. 76.) aci: ateinctum,friet. itir.141111*. iclE11.1.1 111. 77.) tozottegk, mzeauieie. 36& ' U. sit rit -9»:111. al:»ÇM-1-1-eit. 78.) Sti2: *on wear itr• Sttuteetttle, SeLetzte:tt. (tb»atale; 79') en' L f 1 ttelillittaaetat nkgiMille mileage. vie.ttgzst.:kziee. so.) au: VIStit ..i&St*&A1 AWflIA i#ux.». fesitzltitat. En- tt.M: seilisteleoge. I'-emtt.

(Japanese References)*

1.) Ijima: Source of Bothriocephalus latus in Japan. Rika Daigaku Kiyo (Bulletin of the College of Science), Vol. 2. 23.) Parona, E.: Il Bothriocephalus latus in Lombard. Rend. R. Istit. Lomb. (2) XIX. - -Sulla quest. d. Bothr. latus Gazz. med. ital. lpmb. 1886 (according to a reference).

42.) Yoshida: Ueno dobutsuen nite etaru jochu (Tapeworms obtained at the • Ueno Zoo). Dobutsugaku Zasshi (Zoological Magazine), No. 256, 1909. *Translator's note: Including references where Japanese words appear. • Page 104 52.) Eschrecht, D. F.: Anat. -phys. Untersuchungen uber die Bothr. N. Act.

Ac. Canes. Leop. Carol. nat. curios. XIX. Suppl. II, 1814 (according to Ref.). 57.) *• 66.)Willis, H. Rich: Returns from the experiments on the marking of young chinook salmon on the Columbia River. U.S. Bur. Fish. Econ. Cire. No. 45 (according to ref.)

67.)Tanaka: Gifu-ken gyorui zoho (Illustrated report on the fishes of Gifu

Prefecture). Dobutsugaku Zasshi (Zoological Magazine), No. 244** 68.)Koshida: Sakemasu yoshoku (The breeding of salmon and trout). 1915. 69.)Tanaka: Nippon gyo[ruilgaku (Ichthyology in Japan). 1921. 70.)Fujita: Nippon tansui suisan dobutsugaku (The study of the freshwater aquatic organisms of Japan). 1919. 71.)Fujita: Suisangaku Tsuron (An introduction to fisheries science). 1913. 72.)Kokubo: Nipponsan Chikuropusu zoku (Cyclops native to Japan). Dobutsugaku Zasshi (Zoological Magazine), No. 280, 1912. 73.) Ijima: Jintai dobutsu hen (Chapter on organisms in the human body).

74.) guchi: Jintsu-gawa san masu in okeru kosetsu retto jochu yochu (Plerocercoid) kisei no kenkyu (Studies on the larvae (plerocercoids) of Dibothriocephalus latus infecting masou salmon in the Jintsu-gawa). Aichi

Igakkai Zasshi (Journal of the Aichi Medical Society), Vol. 29, No. 4.

*Translator's note: Mbstly illegible on photocopies supplied for translation. From the few words that can be read it would appear that this paper (by Tomikawa? Miyagawa?) is a review of the work done by Japanese researchers in the field of parasitology up to 1924. **Translator's note: No year shown. • Page 105

75.)Eguehi: Kosetsu retto jochu no kenkyu, dai ikkai hokoku (Studies on Dibothriocephalus latus), Part I. Byori Gakkaishi (Journal of the Japan Pathology Association), Vol. 13, 1924. 76.)Eguehi: Kosetsu retto jochu no kenkyu, dai nikkai hokoku (Studies on Dibothriocephalus latus), Part II. Byori G8kkaishi (Journal of the Japan Pathology

Association), Vol. 14, 1925."

77.)Eguehi: Kosetsu retto jochu no kenkyu, dai sankai hokoku (Studies on Dibothriocephalus latus), Part III. Aichi Igakkai Zasshi (Journal of the Aichi

Medical Society), Vol. 31, No. 6 (summary), 1924. 78.)Eguehi: Kosetsu retto jochu no kenkyu, dai shikai hokoku (Studies on Dibothriocephalus latus), Part IV. Aichi Igakkai Zasshi (Journal of the Aichi

Medical Society), Vol. 32, No. 6 (summary), 1925. 79.)Eguehi: "Rigura n-jo yo retto jochu ni kansuru kenkyu hoi (Supplementary

studies on Ligula-like plerocercoids). Byorigaku Kiyo (Bulletin of Pathology, Nagoya), Vol. 2, No. 2, 1925.

80.)Eguchi: Yaju koto ni moju kiseichu to jintai kiseichu to no sogo kankei ni tsuite inchini no chiken zoho (Some supplementary information on the inter-

relationships between human parasites and animal parasites, particularly those

of wild animals). Aichi Igakkai Zasshi (Journal of the Aichi Medical Society),

Vol. 32, No. 6, [1925]. 81.)Eguchi and Kitami: Nagoya shiritsu dobutsuen yaju no kiseichu (Parasites

of animals at the Nagoya Municipal Zoo). Aichi Igakkai Zasshi (Journal of the • Aichi Medical Society), Vol. 31, No. 6, 1924. O Page 106

PLATES

Fig. 1. Fig. 2.

Fig. 8. •

Fig. 5.

4 • O Page 107 Fig. G. Fig. 7. in

•

Fig. 9.

• • Page 108

Fig. 10.

Fig. 1 1.

Fig. 12. Fig. I.

pr • • Page 109 Fig. 14. Fig.. 15. Fr

; cr 7.1 ' F REVISEE TRADUCT;ON Fig. 16. sculz.nleig. 17. Informa'À

O • Page 110

Fig. 19.

•

Fig. 20, Pig. 21. PI

• O Page 111

EXPLANATION OF PLATES

Plate I. Fig. 1. A plerocercoid in the muscle of a masou salmon. Specimen viewed with the naked eye. (Cross-section of encysted plerocercoid). Fig. 2. Same as above. Fig. 3. Complete view of a plerocercoid, under weak magnification (Both. = bothrium). Fig. 4. The head area of a plerocercoid (Zeiss. 2. AA.). Fig. 5. Cross-section of the head area of a plerocercoid (Zeiss. 2. AA.). Plate II. Fig. 6. Histological section of a plerocercoid infecting the muscles. (Zeiss. 2. AA.). Fig. 7. Saine as above. Pl. = plerocercoid, m = altered muscle fibers (The plerocercoid shown in Fig. 6 was obtained from a masou salmon caught in the Shirakawa River). Fig. 8. Same as above. K = a connective tissue-type cyst has formed around [the plerocercoid]. Fig. 9. An adult tapeworm obtained when the author himself experimentally ingested a plerocercoid from a masou salmon caught in the Jintsu-gawa. Plate III. Fig. 10. Eggs in which a six-hooked larva has formed and eggs after the six-hooked larva has been liberated. Two types of eggs are shown, one type having a nodule at its posterior end and another type lacking such a nodule. (Zeiss. 2. DD.). Fig. 11. A six-hooked larva after it has emerged from the egg. (Zeiss. 2. Immelsion.). Fig. 12. Shows the penetration of a procercoid into the body of a Cyclops leuckartii copepod. (Zeiss. 2. AA.). Fig. 13. Shows the penetration of a procercoid (pr) into the body of a Cyclops sternuus (cy) copepod. (Zeiss. 1. AA.). Pr. = procercoid C. = calcareous bodies within the larval tapeworm's body. • ,

• Page 112 Plate IV. Fig. 14 - Fig. 17. Show procercoids (pr) that have grown within the body of a Cyclops. ' Fig. 14 - Fig. 15. Very immature larval tapeworms (procercoids) /p. 66 can be seen, ones in which calcareous bodies have still not formed. Some of these procercoids have assumed an elongated ellipsoidal shape, while others have become constricted at the area where the hooks (h) occur so as to form a spherical body which is attached to the-main body of the larva. In still others can be recognized depressions which represent rudimentarily developed bothria (both). Fig. 16 - Fig. 17. Larval tapeworms that have attained full development in the body of a Cyclops. Numerous calcareous bodies (c) can be seen within the bodies of some of these procercoids (pr), ones in which a spherical body (hp) that possesses hooks (h) has already become constricted to the point where it has detached from the main part of the larva's body. Plate V. Fig. 18. A plerocercoid (pl) that has infected an artificially hatched rainbow 411, trout under experimental conditions. Fig. lg. Cross-section of a complete plerocercoid that has infected an artificially hatched rainbow trout under experimental conditions. (Zeiss. 4. PA.). Fig. 20. An immature plerocercoid that has infected the muscles of a grass carp under experimental conditions. (Zeiss. 2. PA.). Fig. 21. An immature plerocercoid that has penetrated into the stomach wall of a grass carp. (Zeiss. 2. AA.).

„ • Page 113 TABLES

(Translator's note: Only two of the tables have been translated, since the others either; (a) essentially repeat information that is provided in the text; or (b) pertain strictly to the conditions that prevailed in Japan or Europe 60 to 100 years ago)

Table 12 Measurements Made on Larval Tapeworms

PIC> el fill Cle et eAe (.1:-) 0405) ezie, ee ie 1 • 5.° 2.0 25.0 0.9

2 6.o 1.9,5 19.0 049

3 7:3 ..2.0 18.0 113

4 2.* le 10.0 • 0.5 • . s 80 1.2 15e1 0.5 6 6p 24 ee 0.3

7 5.0 le 1 5.0 0.5

8 7.0 1.5 :gm

9 2.5 17.0 I 10 1.5.0 1.5 40.0 1.0

IS 4.0 1.5 25.2 e.35

12 'SA 1.5 27.0 04

13 3.0 1.0 1 7.0 0•35

1 4 5.0 1.2 25.0 0.35

15' 6.o le • :se 0.35 , 16 10.0 1.3 20.0 0.3

. 17 4e 1.25 27.0 0.3

5.0 • a. 1.5 20.0 0.35

19 3.5 1 .35 18.0 0.4

30 6e 14 22.0 0,4

21 9e 1.9 Pe 0.5

22 6e 1.05 23.0 0.5

• 23 10.0 1.0 *re 0.5

3.0-15.0 1.0 • 2.0 40.0-10.0 0.3-1.0

jig..«Â 6.33 1.49 21.83 2.52

t.

• Page 114 (Legend for Table 12) A: number B: when contracted C: when extended D: length E: breadth (i.e., their "short" direction) F: overall range G: average

Table 14 EXperiments on the Resistance Exhibited by Plerocercoids [of D. latus] Experimental Number of Number of Year Procedure Duration Tests Larvae Results 1922 steeped in brine 1 day 1 1 survived 2 days 3 9 survived packed in ice 5 days 1 5 survived in rotten flesh 5 days 1 5 survived 1923 kept in ice house 3 days 2 7 survived packed in ice 2 days 4 23 survived 3 days 2 2 survived It soy sauce 10 min 1 1 contracted, survived 20 min 1 1 contracted, survived 1924 packed in ice 2 days 2 4 survived 3 days 1 6 survived

sanbaizu.(sauLe ee sake, 10 min 2 2 contracted, soy gmd vittelar survived I' artificial gastric 6 hr 1 1 survived juice I' artificial intes- 6 hr 1 1 survived tinal juice n boiling water 5 min 1 I died H II 11 10 min 1 1 -ffiéél n smoked [fish] meat 5 min 1 I survived n n n n 10 min 1 1 died Page 115

(Translator's note: The map appended to the text has not been translated.)

•

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lee

111

tei

d 011 ..... ga rp • 7,11 le « r- e -F oral& 41 le 1.11M L.--

it &II le A 4. ..A. e _ e e e • ..... ec . >IF — / *rug / (.7 / /wig' .....

a lbr Itfis

eSï • 5 111