Translation Series No. 580

5'gû THE LIBRARY - 4 FISHERIES ARCHIVES REZCZCii 10.IRD OF CANADA NANAIA40,

FISHERIES RESEARCH BOARD OF CANADA Translation Series No. 580

Morphological changes in the fish tissue surrounding the larvae of certain parasitic worms

By I. G. Mikhailova, E. V. Prazdinkov, and T. O. Prusevich

Original title: Morfologicheskie izmeneniia v tkaniakh ryb vokrug lichnok nekotorykh paraziticheskikh chervei.

From: Trudy Murmanskogo Morskogo Biologicheskogo Instituta, Vol. 5, No. 9, pp. 251-264.

Translated by G. N. Kulikovsky, Bureau for Translations, Foreign Language Division, Department of the Secretary of State of Canada

Fisheries Research Board of Canada Biological Station, Nanaimo, B. C. 1965 Morphological Changes in Fish Tissue around 251 the Larvae of some Parasitic Worms.

By I.G. Mikhailova, E.V. Prazdnikov, and T.O. Prusevich.

(Laboratory of Comparative and Experimental Embryology. Chief - B.P. Tokin.)

(From "Trudy Murmanskogo Morskogo Biologicheskogo Institute" /iransaction of the Murmansk Sea-Biological institute/, USSR Academy of Sciences, No. 5 (9) p. 251-64).

The problem formulated in the Thirties by E.N. Pavlovsky: MDrganism as the medium of habitation" (1934, 1937, 1945) acquires an ever-increasing actuality. As a point on the agenda the necessity remains to mobilize the assistance of other Sciences for its solution:- of Experimental Zoology, General Pathology, Biochemistry, Immunology, and of Microbiology. New ways of consider- ing the interrelations between the parasite and the host also appear on the borderline between parasitology and embryology.

A successful method of study of the problem of the immunity of the embryos (Tokin, 1955a, 1955b) is primarily a study of the problem of embryology - a problem of interrelation of at least two organisms: of a macroorganism and microorganism. In the light of ideas developed by B.P. Tokin, the interrelation between the parasite and the host, in particular between the host and the larval stages of the parasites, deserve special attention, because: "a parasite, which in the course of evolution has found itself in another body, which is to the former, both a medium of habitation and food, cannot be merely an enemy to the host. With a certain foundation, one may speak conditionally about the host as being the enemy, and furthermore, - a very dangerous enemy to the parasite" (Tokin, 1955a, page 10). Being in possession of the knowledge concerning the 2/251-252 immunological properties of the host and of the parasite, one could, by increasing the defensive reaction of the host and by decreasing the immunological reaction of the parasite, annihilate the later. The facts, concerning the destruction, incapsulation, or phagocytosis of parasites inside the body of the host, are commonplace. Nevertheless, we still know next to nothing about the causes of the death of a parasite.- in some cases, and of a normal development and preservation in the tissues of the host, - in other cases. It is not accidental that, when discussing the problems of interrelations between the host and the parasite, the parasitologists do not fail to •note the necessity for taking the immunological features into account (Shuurmans-Stekhoven, 1955; Schultz, Davtyan, 1954, 1955; Shikhobalova, 1950; Naumova, 1955; Bauer, 1958; Markov, 1958, and others). At the same time, the morphological studies of the defensive reactions of the tissues of the host and of the parasite are feN, and they are either descriptions of individual casuistic cases (Heim, 1954; Tratnig-Frankl, 1956), or a supplement to the parasitological or zoological observations of the authors. Extremely controversial ideas were developed by V.A. Fausek (1903, 1913), who tried to draw a direct analogy between parasitism and viviparity. However, Fausek must be credited with being the first to give special attention to the utilization, by the parasitic organism, of the inflammation processes in the tissues of the host for the purpose of feeding. In the work of R.M. Lewert and Lee Chang-Ling (1954) interesting 252 data concerning histochemical changes in the host's tissues around the larvae of the parasitic worms are presented. There are detailed descriptions in the literature of various interrelations occurring between the tissues of the host and the larval stages of the parasitic worms, primarily in 1.1ch intermediate hosts as mollusks (Agersborg, 1924; Rees F.G., 1934; Rees W.J. 1936, and others). In a work by E.A. Zelikman "Certain ecological-parasitical connections on the littoral of the northern portion of the Kandalaksha Bay" (1955), one may find rather complete accounts of bibliographical data available on this problem. E.A. Zelikman, just as other scientists, observed the destruction picture of 3/252

the visceral complex of the mollusks in the development of the sporocysts and rediae. The author describes cases of antagonistic action of one parasite upon another at double invasion. In the works of E.D. Logachev (1956, 1961), of Logachev and N.A. Fedyushkina (1955), of Logachev and B.R. Bruskin (1959), peculiar multinuclear structures are described, which originated in the tissues of a mollusk pro- duced by a parasite. Efforts are made to establish, how the reparative processes . run in the parasitic worms. A large number of observations indicate that the character of the membranes and capsules, originating near the endoparasite, change considerably in case of a change in the life functions of the host or the parasite. When the parasite dies, there is either a resorption of the latter by means of the phagocytes of the host, or the remnants of the parasite are enclosed in a dense fibrous capsule, which is later permeated with calcium salts. The data concerning the interrelations of tissues of haddock and cod, with the larvae of nematoda selected by us for the experiment (Anisakis . sp., Contracoecum aduncum, Terranova decipiens) and of the cystoda (Pyramico- cephalus phocarum, Bothriocephalus sp.) may be found in the works of a number of researchers. A.Ya. Bazikalova (1932) points out the pathological importance of parasites and the reactive changes owing to their influence in the organs of the host. Thus the plerocercoids (Cestodes gen. sp.) produce considerable changes in the liver of haddock and cod. The colour of the liver turns dark red, irnd the plerocercoids degenerating in the parenchyma are surrounded by voluminous hardenings of irregular shape. Bazikalova writes that similar formations, something like cases of smaller size, are also formed around the larvae of the parasitic nematodes Anisakis sp., Contracoecum aduncum. The total weight of the parasites in the Gadidae, according to the observations of the author, does not exceed hundredths or thousandths of one per cent of the total weight of the body of the fish. The larvae of the Cestodes produce a more destructive effect upon the tissues of the host, than do the larvae of the nematodes, particularly when localized in the liver. Bazikalova believes that the basic pathogenous effect is supplied by the toxines of the parasites, these toxines produce partial destruction 4/252-253 and regeneration of the host's tissues. The weight of the haddocks and cod's liver decreases with the increase of the number of parasites, the fattiness also decreases (the relation between the weight of the liver and the weight of the fish). The author came to the conclusion, that parallel with other aspects of the study of the problem of the character of the effect of the parasites upon the host's body, the histological changes, particularly those originating as the result of the affection of the liver by the parasites, deserve special attention. S.S. Shulman (1948, 1958), R.E. Shulman (1950), S.S. Shulman and R.E. Shulman-Albova (1953) record the infestation of the liver of the Gadidae by Contracoecum aduncum and by Anisakis sp. The weight of the liver decreases in the affected fish. The most distinct decrease in the weight of the liver presents itself in the largest specimens (haddock and cod between 1 and 253 2.5 kilograms). The celozoic parasites in the Novaya Zemlya char (Dogel and Markov, 1937) change in connection with the migration from fresh to sea water. The autumn chars are not infested with Bothriocephalus, and the summer chars are not infested with Contracoecum. This phenomena, together with some very interesting observations by a number of authors, including Polyansky (1955), concerning the decrease, in the winter time, of the infestation rate of cod and haddock with celozoic and intestinal parasitic nematodes (Contracoecum and Anisakis), still remain unexplained. Thus, despite the agreement of the majority of the parasitologists on the importance of the morphological studies of the reactive changes originating in the organs of animals infested with endoparasites, this side of the problem remains poorly studied. The aim of the present paper is the study of the morphological characteristics of the capsules around the larvae of certain parasitic worms in the tissues of fish, mainly of haddock (Melanogrammus aeglifinus), cod (Gadus morhua morhua), shorthorn sculpin (Myoxocephalus scorpius), and also partly of the arctic char (Salvelinus alpinus). Capsules were studied in the liver and the mesentery of the haddock, cod, sculpin, and char. The length of the studied fish was: haddock and cod - 20-50 centimeters, sculpin - 20-30 centimeters, and char - 25-30 centimeters. 5/253

Organ parts with larvae of parasitic worms were prepared in Bouin solution, in zenker-formol, Carnoy's solution, and in 10% formalin. The best results were obtained from the treatment with Bouin and Carnoy.'p .: solutions. Fragments were poured over by celloidin-parafin and by celloidin. The sections were stained by the Mallory method and with resorbin-fuchsin by the van Gison method; they were silvered according to Foot's method; stained by means of Hansen's trioxihematein, and also with picro-fuchsin. In the liver of haddock and cod, and also of the shorthorn sculpin one may find a considerable number of larvae of Anisakis sp., Contracoecum aduncum, and less frequently of Terranova decipiens. Detailed analysis of the intensity of the infection of this organ in the haddock, cod, and sculpin may be also found in the works of A.Ya. Bazikalova (1932), S.S. Shulman (1948), S.S. Shulman and R.E. Shulman-Albova (1953), and Yu.I. Polyansky (1955). In the present paper we describe the morphology of certain age- changes ir the capsules in late stages of development on the basis of histological analysis of 38 cases of the liver infection of the cod, haddock, and sculpin by the larvae àf the Nematodes, and in 8 cases - by the larvae of the Cestodes. . Bodies of the anisakid larvae in the vast majority of cases are encapsulated and wound up in spiral form. In the parenchyma of the liver, in places where the parasite is located, one observes impressions, the 'depth of which corresponds, as a rule, to the thickness of the capsule, which repeats the windings of the larval body. It should be noted, that when the parasite stays longer, these impressions are expressed more sharply. The formation ()If the capsule, obviously, takes place in the following manner. The larvae of Anisakis sp. and Contracoecum aduncum attach themselves to the surface of th'e liver, thus they compress and mechanically damage the serous membrane and the adjoining portions of the liver parenchyma. Besides the mechanical factor, the products of the life of the larvae obviously also have effect upon the adjoining tissues. All this leads to the reactive hypertrophic growth of the fibroblastic elements and to the accumulation of the cells of hematogeneous origin. The insignificant distrophic changes in the adjoining liver cells also take place simultaneously. The juxtaposition of the thickness of the relatively "normal" serous membrane of the liver of the haddock and the and the relatively still "young" capsule of the connective tissue, 6/253-256 appears extremely demonstrative (fig. 1, 2). The serous membrane near the larva becomes tens of times thicker. The age of the capsule in each observation case remains unknown 254 to us, but the studied capsule may be morphologically distinguished into two groups: the "young" and the "old". This division is also supported by the experimental data on the study of the formation rates of the capsules (Prusevich, in the present compendium). Morphological changes occurring in the serous membrane and in the adjoining sections of the liver parenchyma, when the larvae of Anisakis sp. and of Contracoecum aduncum are present, are similar in many respects, - in both cases a capsule of connective tissue develops near the larvae, at the expense of the hypertrophic changes in the serous membrane of the liver. Larvae of the parasitic nematodes plunge into the glandular tissue of the liver (fig. 3) and produce insignificant local degenerative changes. We shall not dwell on the differences in the reactivity of the liver tissues of the haddock, cod and sculpin, when responding to the invasion of parasitic larvae, because we observed comparatively monotype changes in the connective tissues of this organ and in the liver parenchyma, except in a few cases, when we observed in the liver of cod extensive infiltration of tissues of the capsule by the leucocytes. The morphology of the capsules around the larvae of the Anisakis sp., and of the Contracoecum aduncum does not differ in principle. We present here a description of the capsules, which originate around the larvae of Anisakis sp., since we possess considerable amount of material on the development of capsules of this species. By histological analysis one is able to distinguish in a "young" capsule formed near the larva of Anisakis sp., conditionally and morphologically, at least three layers of connective tissue. The first layer which directly contacts Anisakis sp., is a narrow strip of tissue consisting of damaged cellular elements with traces of pyknosis, and sometimes of the lysis of the nuclei. Here the collagen fibrills are homogenized and in spots the entire basic material of the connective tissue is intensively tinted with acid stains (fig. 3, 4, and 5). 256 Behind the layer of damaged tissue follows a second layer with a greater quantity of fibroblastic elements, these are partly subjected to 7/256-257

degenerative changes. The nuclei of the cells of this layer are light coloured, sometimes bacilliform, often unusually elongated (fig. 5). It is known, that the nuclei of the fibroblasts of the mammals take such a shape when damaged. Pictures of fragmentation and amitotic division of the nuclei of the fibroblasts are often observed. Collagen fibril's occur among the cellular elements of this layer. The third layer usually consists of porous connective tissue (fig. 4). It contains numerous blood vessels, diverse cellular elements, among which often occur histiocytes, large fibroblasts with a clearly pronounced diplas- matic differentiation. Amitotically dividing fibrocytes are visible in certain preparations. Among the cell elements there frequently occur leucocytes, extra-vascular erythrocytes, and remnants of destroyed erythrocytes, which are like pigment grains. In places where the thin connective-tissue lacerti which encase the body of the larva depart, original widenings occur, at the base of which one often observes blood or lymphatic vessels. At the border of the liver parenchyma there is a relatively unchanged more solid connective tissue, which reminds us of an externally normal serous membrane. Individual elastin fibres are observed in the third layer, but they are very few in number, and probably do not have any significance in the formation of the capsules. Possibly, this is connected with the fact that the larvae of Anisakis sp. are immobile in the fish tissues. The liver tissue adjoining the connective-tissue capsule of the larva is very little changed campared to the other part of this organ, except for a stronger development of the connective-tissue interlayers and except for their more numerous content of blood vessels. The basic connective-tissue "skeleton" of the cod and goby liver 257 are the argyrophyl tissues and granules, which are particularly numerous along the course of the capillaries. Thin collagenous fibrills occur along the course of the blood vessels, and are sometimes observed between the cells of the liver. The most numerous collagenous bundles are located near the large blood vessels and in the serous membrane of the capsule. The argyrophil fibres were studied inside the capsules near the larvae of the nematodes in the liver of cod and sculpin. In both cases their analogous 11.1 arrangement was observed. Individual argyrophil granules occur in the first layer. In the second layer we see numerous small argyrophil granules, sometimes the argyrophil substance is deposited near the nuclei of the 8/257-258 degenerating cells. The argyrophil granules are most numerous of the capsules of the nematode larvae in the sculpin, where the second layer is sharply distinguished from the third layer, because of the presence of fine argyrophil granularity in the second layer. In the third layer argyrophil fibres occur, these form retiform structures in some areas. At the border with the second layer, in a number of cases there originates an interlacing of argyrophil and collagen fibrills. At the border with the parenchyma of the liver, the argyrophil fibres arrange themselves along the periphery of blood vessels. With the increase of the period of stay of the Anisakis sp. in the serous membrane of the liver, the connective tissue grows in the adjoining sections. An increasing number of blood vessels penetrate into the capsule. As a result of intra-abdominal pressure, and, probably, also because of the local deceleration in the growth of the liver tissue, the nematode together with connective-tissue capsule plunges deeper into the liver parenchyma. Along the course of the blood vessels the thickness of the connective tissue interlayers increases, and a part of the blood vessels penetrate from the parenchyma into the capsule. The connective-tissue "casing", which repeats the helices of the larva, appears distinctly in the histological sections. In "older" capsules the morphology of individual layers is somewhat different. The basic substance of the connective tissue appears in the first interior layer, it is homogeneously tinted over with orange-yellow colour. The cell elements disappear from this layer. Between the first and the second layer (the layer of the fibroblastic elements) appears a narrow strip of tissue, which does not contain cell elements, which, according to Mallory, is tinted in lilac hues, and which sometimes shows fibrillar structures. In the second layer one observes the destruction of a part of the cells. This layer has no distinct borders and blends with the first layer, and is probably 258 permeated with calcium salts. The third layer is the widest one; two zones are observed in this layer (fig. 6). In the first zone, which adjoins the second layer, we find blood vessels. In the connective tissue degenerative cell elements, the more or less numerous errant cells, are observed (fig. 6, 7). In preparation stained with picro-fuchsin, the homogenized collagen bundles are seen in this zone. Sometimes the basic substance is homogeneous and is poorly stained with acid fuchsin. In these cases, the homogenized collagen substance is obviously formed. In the second zone, at the border to the 9/258-259

liver parenchyma, wide collagen bundles are arranged. In cod and haddock these bundles are like intertwining ribbons, while in the shorthorn sculpin collagen window-like membranes appear. At the described stage of development, the capsules separate easily from the serous membrane of the liver. To clarify the formation rate of the capsules around the larvae of parasitic nematodes, we have carried out tests on transplanting of larvae of Anisakis sp. from cod to sculpin. To obtain the larvae, we utilized their ability to leave the tissues of a dead host. For this purpose a liver removed from a cod, which was infested with encapsulated nematodes was placed in an aquarium with running water. During the fifth to eighth days, we observed active exodus of the continuously moving larvae from the capsules, and their falling down to the bottom of the aquarium. Simultaneously conducted histological analysis of the disintegrating capsules and adjoining sections of the liver, has shown that during the sixth to eighth day the glandular elements of the liver are necrotized and partially undergo lysis. The bearing structure between the liver cells is well preserved in the serous membrane and in the walls of the blood vessels. Collagen fibres are distinctly tinted according to Mallory. In the liver tissues, particularly in the connective-tissue interlayers, a large number of microorganisms appears. The first (interior) layer of the capsule is completely dissolved, and the major part of the thin partitions is destroyed. In the second and third layers the collagen skeleton is preserved in the latter's thinnest sections. Some of the collected parasites were killed by means of 5-minute long boiling prior to their introduction into the abdominal cavity of the sho:rthorn sculpin. Several hours before the operation the live and the killed larvae of the nematodes were dipped into a dense batch of carmine dissolved in sea water. The carmine permits us to follow the phagocytic processes in the formed capsules, and serves to mark the introduced larvae. The laparatomy was carried out without narcosis and without any strict observance of the rules of aseptics. The nematoda larvae were placed between the interior surface of the abdominal wall and the liver. A total of 20 sculpins were oper- ated. Into some of the fish two live larvae were introduced, while in the 259 others - two boiled larvae into each fish. The histological discription of the capsule formation is presented in a paper of T.O. Prusevich (in the present compendium). 10/259 •••

The formation rate of capsules in both cases was the following. After introduction of live larvae, within 4 hours after the operation, half of the larvae were already attached, as a rule, to the serous membrane of the liver. After 6 hours, almost all the larvae were attached, and some of them were already rolled up in spirals. After 12 hours the bodies of introduced anisakid larvae were surrounded by a thin membrane, the latter had to be broken in order to remove the nematode from the liver. After 24 hours and later, the larvae were fully fixated upon the serous membrane of the liver, or upon the abdominal wall of the body. It is very interesting, that encapsulation of identical larvae, but which were first killed by boiling 5 minutes (10 tests) is much slower. Six hours after the nematoda bodies were introduced into the cavity, they were still lying. freely, and only after 12 hours commissures with the serous membrane of the liver took place. The analysis of data available to us . permits us to conclude, that around the larvae of parasitic nematodes original connective-tissue capsules are formed, which differ considerably from the capsules developing in the fish tissues as a response to the introduction of relatively indifferent foreign body, for example introduction of a celluloid tube (Zavarzin, 1937, 1938). It seems that the life products isolated by the nematoda larvae do not permit the host's tissue to form a dense fibrous capsule, which isolates completely the parasite's organism. The products of the life-activity of the larvae of the parasitic nematodes provoke continuous destructive changes of the cellular and fibrous elements of capsules, and also chronically running proliferative processes - a continuous formation of new fibroblastic layers, growth of blood vessels, and accumulation of numerous and diverse phagocytes. Capsules originate around the nematode larvae; in these capsules, the inflammatory and regenerative reactions in the host's tissues are utilized by the parasite for the purpose of alimentation, excretion, and defence from the phagocytes. The absence of dense fibrous capsule enables the larvae of the parasitic nematodes to leave the capsules. In addition to the liver, we have also studied the capsules around the larvae of Anisakis sp. and Contracoecum aduncum in the serous membrane of 11/259-260. stomach and of the intestines of the haddock and cod. We distinguish the above-described layers in these capsules. However, the second layer is less pronounced, and in some cases it is absent. In the capsules there is more porous connective tissue and relatively many diverse wandering cell elements, particularly in the third layer. The wandering cell elements of hematogenic and connective-tissue origin are numerous. According to the data of Lyu (1960) the inflammatory reactions in the serous membranes of the mammals run extremely intensively, and in the infiltration by the cell elements is always very acutely expressed. Obviously, analogical regularities are also observed in fish. However, changes in the connective tissue around the parasitic nematodes, in the liver and in the serous membrane of the stomach and of the intestines, are similar in many respects. Let us dwell briefly on the changes occurring in the liver, when the larvae Terranova decipiens had entered. The latter, in a vast majority of cases, locate themselves deep in the parenchyma of the liver. Near the larvae of Terranova decipiens in the sculpin's liver, regular morphological changes are observed. In the very earliest stages of the invasion the blood vessels are destroyed and the liver cells are com- pressed. For a considerable length along the body direction, the liver 260 cells become fusiform with round light nuclei. A part of the cells are vacuolized, the traumated cells perish. Sections of disintegrated cell elements of the liver are observed, among these cell elements one may see cells of blood, fibrin, and of tissue detritus. The presence of formed capsule consisting of cells of connective tissue and of hematogenous origin, and also of the fibrous structures is, however, very common. Between the original capsule and the larva body appears a granular mass with fibrin clots, fragments of liver tissue, and with detritus. In the capsule3one may distinguish the first layer of tissue elements, which is in direct contact with the larva and which consists of homogenized tissue of fusiform cells with pyknic nuclei. Many of the cells die off. Probably, this layer is fully comparable with the first and the second layers of the capsule in the liver near the larvae Anisakis sp. and Contracoecum aduncum. One may assume, that the fusiform cells belong to the fibroblastic elements. A peculiarity of this layer is the presence of 12/260-261 fibrin in areas bordering between the cuticula of the larvae, and the liquid, which fills the lumens between the surface of the parasite and the cell layers. The second layer consists of fibroblasts, leucocytes, and phagocytes of various origin. The width of this layer is changeable. In certain areas of the capsule this layer may be absent, but where it is well defined, one almost always manages to distinguish within it two zones. One zone is the interior zone, which is immediately adjoining the first layer, and this zone contains no collagen fibres; the other zone - the exterior one, contacts immediately the liver cells and forms the basic mass of the second layer; it contains wide homogenized collagen bundles, in which individual collagen fibrills and capillaries are sometimes observed. Here in some sections one may also see large blood vessels with thrombi or in the collapsed state. Around the collapsed blood vessels grow muscle fibres of the middle membrane of a blood vessel; giant cells with round, light nuclei appear. In , the second layer of the capsule accumulations of phagocytes with cytoplasma take place, which may be easily coloured by Hansen's trioxihematein. Granules of brown pigment occur everywhere; analogous granules are also observed in the intestines of Terranova decipiens. The liver cells, which are in contact with the connective tissue of the capsule, are usually little changed. However, in certain cases we succeeded in observing in the border layers, groups of liver cells, which 261 are smaller, with more basophilic cytoplasma, which contain almost no adipose inclusions. Probably, the appearance of similar cells should be considered as a reflexion of the reactive phenomena on the side of the liver parenchyma. In the alimentary tract of the larvae of Terranova decipiens a tissue detritus, fibrin clots, and sometimes individual liver cells and erhythrocytes are observed. The bacteria are very common in the intestines of the larvae. The comparison of the reactivity of the tissues of haddock and of cod towards the intrusion of nematode and cestoda larvae presents a certain interest. We had plerocercoids of Pyramicocephalis phocarum in the liver of these fish. The plerocercoids were surrounded by connective tissue, and, in some areas, they were in immediate contact with the liver parenchyma. The liver tissue near the plerocercoids was deformed. In a number of cases the liver beams (Trt meaning not clear) were arranged very loosely, they were 13/261-262 stretched around the plerocercoids, a number of liver cells were found in a distrophic condition. Around the larvae of tape worms one may conditionally distinguish three layers. The first and the interior layer consists of damaged connectiv e . tissue and liver cells, the latter are often vacuolized. In areas at the border with the plerocercoid, especially in the "older" capsules, the cell elements of the liver parenchyma are completely destroyed, while the basic substance of the connective tissue is hyalinized in the same manner, as in the capsule near the nematoda larvae. The second layer is particularly well developed and consists of porous connective tissue with numerous blood vessels (fig. 8 and 9). A large number of wandering cell elements are recorded, extravasates occur and are particularly extensive, probably, in the early stages of the instrusion of the plerocercoid. The third layer consists of a relatively little changed specific tissue of the organ. In this layer one is able to note only few enlarge- ments of the blood vessels. Thus, around the larvae of tapeworms (Pyramicocephalus phocarum) the proliferative reaction is expressed less vividly, regardless of the fact that the plerocercoids are inside the liver tissue, their cuticula in some areas is in immediate contact with the glandular cells, and the parenchyma of the liver IsEubjected to morphologically expressed distrophic changes. In this connection it is necessary to remember the tests of K.P. Villako and L.A. Villako (1960) Dunning and Cutris (1953) on isolation of biologically active substances from the tissues of the tapeworms. It may 262 be assumed, that the considerable deformation and reduction of the reactivity of the tissues of the host's organism near the larvae of the tapeworms, is connected exactly with the isolation of this type of substances into the surrounding medium. In the mesentery of a char (fig. 10) we sometimes observed very numerous capsules with plerocercoids (Bothryocephalus sp.). In the histological sections a similarity is observed to the conditions described above. One of the distinctive traits of the capsules is the considerable quantity of the leucocyte elements in the connective tissue. 14/262-263

Of great interest is the fact, that the morphological peculiarities of the capsules formed around the larvae of the tapeworms in such relatively distant classes of the vertebrates as fishes and mammals, are surprisingly similar. The cysticercus Taenia taeniaeformis often develops in the liver of white rats. Similar to that for the plerocercoids of the fish studied by us, three layers, analogous to those described above, may be distinguished in the liver of the white rats. A considerable number of wandering cell elements are observed here; thick Erlich cells are common. In all the cases the deceleration of the development process of the fibrous structures is observed; capsules, similar to the ones formed near the larvae of the parasitic rounchNorms, never occur. Thus, all the capsules around the larvae of parasitic worms studied by us present a considerable similarity expressed through the constant presence of two layers: a layer of distrophically altered tissue at the border with the parasite body, and of a layer of connective tissue with numerous blood capillaries. A considerable number of specific features is also observed in the character of inflammatory reactions depending on the species of the parasite. The capsules originating around the . larvae of the parasitic nematodes and tapeworms, have a number of morphological peculiarities. A peculiar area is formed between the parasite and the host, in this area locally and to different degrees the defensive reactions of the host are suppra7sed and the inflammatory reactions are utilized in the interests of the parasite. Thus the capsules are not protective structures of the host alone, isolating the latter from his enemy - the parasite. When analyzing the above-stated material, one must agree with the ideas of B.P. Tokin, that it is necessary to make closer studies of the immunological features of the host and the parasite. We see, that to the morphologists the efforts of the experimental study of the peculiarities 263 of the attachment and the encapsulation of the tape stages of the parasites under various conditions and in different states of the immunological properties of the host's and the parasite's organism, is highly prospective. At the same time, the task of studying the immunological properties of 15/263

metabolites isolated by the endoparasites, and their e ffect upon the inflammatory and phagocytic reactions of the host's tissues, becomes more and more urgent.

Texts under illustrations

Fig. 1. Section of a haddock's liver. Stained according to Mallory. Enlargement: objective - 3, ocular - 15. 1 - parenchyma of the liver; 2 - dense connective tissue of the capsule; 3 - hyalinized connective tissue of the capsule; 4 - section of the larvae of Anisakis sp.

Fig. 2. Section of a haddock's liver. Hansen's trioxihematein. Enlarge- ment: objective - 20, ocular - 15. 1 - parenchyma of the liver; 2 - serous membrane of the liver; 3 - blood vessels.

Fig. 3. Section of a haddock's liver. Hansen's trioxitematein. Enlarge- ment: objective 20, ocular 15. 1 - parenchyma of the liver; 2 - layer of a relatively little changed serous membrane of the liver; 3 - porous connective tissue of the • capsule; 4 - blood vessel; 5 - layer of degenerating connective-tissue structures. Fig. 4. Section of the haddock liver. Stain according to Mallory. Enlarge- ment: objective 10; ocular - 15. 1 - parenchyma of the liver; 2 - hyalinized connective tissue of the capsule; 3 - connective tissue with coarse collagen bundles and blood vessels.

Fig. 5. Section of a capsule near the larva Anisakis sp. Hansen's trioxihematein. Enlargement: objective 90, ocular - 15. • 1 - layer of degenerating tissue elements; 2 - fibroblast nuclei; 3 - porous connective tissue; 4 - histiocyte; 5 - blood vessel.

Fig. 6. Section of a haddock's liver. Stain according to van Gizon. Enlargement: objective - 20, ocular - 15. 16

1 - parenchyma of liver; 2 - the relatively little changed serous liver membrane; 3 - section of the larva of Anisakis sp.; 4 - connective tissue of the capsule infiltrated by the wandering cell elements. Fig. 7. Section of the capsule near the larva of Anisakis sp. Hansen's trioxihematein. Enlargement: objective - 90, ocular - 15. 1 - collagen fibres; 2 - capillary; 3 - histiocyte; 4 - fibroblast.

Fig. 8. Section of a cod's liver. Hansen's trioxi .hematein. Enlargement: objective - 10, ocular - 15. 1 - parenchyma of the liver; 2 - plerocercoid; 3 - degenerating connective-tissue elements; 4 - porous connective tissue. Fig. 9. Section of cod's liver. Stain according to Mallory. Enlargement: objective - 20, ocular - 15. 1 - parenchyma of the liver; 2 - plerocercoid; 3 - layer of the liver's capillaries. Fig. 10. Section of a char's mesentery. Hansen's trioxihematein. Enlarge- ment: objective - 20, ocular - 15. 1 - plerocercoid; 2 - degenerating connective-tissue elements of the capsule; 3 - connective tissue of the capsule with a large amount of blood vessels.

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