THE ETIOLOGY OF MALABTAL DISEASES. 429 On the Question of Priority with Regard to certain Discoveries upon the ./Etiology of Malarial Diseases. By George If. F. Nnttall, M.A., M.D., Ph.D., University Lecturer in Bacteriology and Preventive Medicine, Cambridge. THOUGH it has long been a popular belief in certain countries that malaria is communicated to man by means of mosquitoes, experimental proof was lacking until a recent date. The history of the mosquito-malaria theory has been amply dis- cussed elsewhere by the writer, to whose papers the reader is also referred for a detailed description of the experimental work on the part played by mosquitoes in the propagation of malarial diseases.1 It is not the object of this paper to discuss these matters in detail. Persons who read the medical literature of but one country will naturally become biassed in their judgment. This ac- counts for the fact that at present different investigators receive the credit of having definitely established the part played by mosquitoes in malarial diseases. In view of the confusion which will naturally result from the claims made i Nuttall, G. H. i\ (1899-1900). I. " On the Role of Insects, Arachnids, and Myriapods as Carriers in the Spread of Bacterial and Parasitic Diseases of Man and Animals: a critical and historical Study;" 'Johns Hopkins Hospital Reports,' vol. viii, pp. 1—154, 3 plates (Bibliography). II. "Die Mosquito-Malaria-Theorie," ' Centralbl. f. Bakteriologie,' vol. xxv, pp. 162— 170, 209—216, 245—247, 285—296, 337-346 (Bibliography). III. " Neuere Forschungen iiber die Rolle der Mosquitos bei der Verbreitung der Malaria: Zusammenlass,endes Referat;" ' Centralbl. f. Bakteriologie,' vol. xxvi, pp. 140—147, and vol. xxvii, pp. 193—196, 218—225, 260—264, 328—340 (exhaustive Bibliography). 430 GEORGE H. F. NUTTALL. in vai'ious quarters, it seems eminently desirable to give a brief impartial summary of the experimental work which has been done, relying solely upon published researches, these being cited in their chronological order. With the facts thus marshalled before him every reader is at liberty to draw his own conclusions. The study of the liEemocytozoa begins with the discovery by Ray Lankester in 1871 of Drepanidium ranarum. Human malarial parasites were seen, but their significance not comprehended until Laveran published his investigations in November, 1880. Following upon, the fundamentnl work of Laveran, the most important discovery was that of Golgi (November, 1885), who demonstrated the relationship exist- ing between the life-cycle of the parasites within the human body and the occurrence of the febrile attack. "With regard to these investigations there has never been any dispute on the question of priority, but this is far froni being the case with the discoveries which followed. Any further disputes regarding the priority of subsequent discoveries should be disposed of by such a chronological record as that which follows, in which not only the year, but also the month and even day of publication are given. Chronology relating to certain of the more Im- portant Recent Researches on Malaria. 1893 and 1895, Sacharoff demonstrated the presence of chromatic substance within the "flagella" of certain avian parasites by means of the Romanowsky stain. December 17th, 1895, Ross observed the process of "flagellation " of crescentic parasites to occur in the stomach of mosquitoes (species not determined) fed on the blood of a malarial patient. 1896, Bignami and Dionisi report the negative results of two experi- ments made in 1893-4 with mosquitoes (species uncertain) collected in malarious localities, the insects being permitted to bite healthy per- sons. They attribute the failure of the experiment to the dispersion of THE ETIOLOGY OF MALARIAL DISEASES. 431 the insects in the room where they were liberated, and to the experiment not having been continued long enough. They cite Calandruccio as having observed the degeneration of malarial parasites in the stomach of mosquitoes (species not stated). November 13th; 1897, MacCallum, in Baltimore, found that the "flagella" of Halteridium and of Eestivo^autumnal parasites constitute the male element, and serve to impregnate the "pig- mented spheres" or female element. In the case of Halteridium the impregnated spheres became con- verted into motile " vermicules." This transforma- tion was, however, not observed in the human parasites. December 18th, 1897, Ross fed mosquitoes upon human blood containing crescentic parasites. The ex- periments were made at Secunderabad, and were reported upon at the time as follows : After examining hundreds of mosquitoes fed on malarial blood, always with negative results, he obtained a few which belonged to a species with spotted wings, which he had hitherto not used. As Eoss distinctly describes the egg of this species, there is no doubt whatever but that he was dealing with a species of Ano- pheles. The insects were bred from larvae, and fed •with blood containing crescentic parasites. Pour to five days later peculiar pigmented cells were obsei-ved lyiug within the walls of their stomachs. These cells were round or oval; they measured 12—16 /x on the fourth, and 20 fx on the fifth day after feeding, and the pigment they contained was similar to that within the malarial para- sites in the blood upon which the insects had been fed. Such bodies could not be found in control mosquitoes. Eoss concluded that he had found the mosquito which served as a host for the parasite. February 26th, 1898, Eoss refers again to his experiments with crescentic parasites. After examining some scores of " dapple-winged" mosquitoes unfed or fed with healthy blood, all the results were negative until 432 GKOfiOK K. F. NTTTTALT,. " at last two of this species were, persuaded to feed on a patient with crescents. One of them was killed next day; no pigmented cells could be found. The second was killed forty-eight hours after feeding ; numerous pigmented cells were pi'esent. They were all small, much smaller than epithelial cells, ovoid, about 7 n in the major axis, and each contained about twenty granules of typical pigment, which were often arranged circmnferentially, just as in the malarial parasite." Though it is not stated in this publication that he raised these mosquitoes from larvae, reference to Boss's previous paper (p. 1786) will show this to have been a part of the method he employed. Experiments with Tertian Parasites.—"A hundred or more grey or 'barred-back' mosquitoes, unfed or fed on healthy or crescent blood, have been dissected without finding the pigment cells. At last one was observed feeding on a patient whose blood that morning had been seen to contain numerous mild tertian parasites." Killed on the third day, the insect contained many pigmented cells measuring 8—25 p, (Ross subsequently discarded this experiment, as it was possible that the insect which was not raised from the larva had become infected with some other parasite.) May 21st, 1898, Experiments on Proteosoma.—Work- ing in Calcutta, Ross observed the development of Proteosoma in a species of Culex (subsequently determined as C. fatigans, Wied.), the insects being fed on the blood of infected crows, larks, and sparrows. The parasites found in the external coat of the insects' stomachs measured 6 fi after thirty hours, 60 (i after six days. "Successive feeds by the same mosquito on the same bird are followed by fresh crops of young coccidia. Similar pigmented cells" had been previously observed in mosquitoes fed on human parasites. Ninety- four per cent, of the mosquitoes fed on blood containing mature Proteosoma became iufected. September 24th, 1898.—Manson reported to the British THK ^ETIOLOGY 01' MALAHIAL DISEASES. 433 Medical Association Meeting at Edinburgh (July) on behalf of Boss regarding further experiments with Proteosoma. These observations showed that the encapsulated parasites, on reaching a certain size, rup- tured and emptied their contents into the coelom of the insect. The contents of the ruptured capsules consisted of minute spindle-shaped bodies, and these bodies sub- sequently accumulated in the salivary gland of the insect. When this had occurred the insects were capable of communicating the proteosomal infection to healthy birds. Of twenty-four sparrows exposed to the bites of insects fed on matnre parasites, twenty-two became infected. October 1st, 1898, Grrassi reported that he had reason for suspecting three species of Culicidae as being carriers of malarial infection, claiming that they were confined in their geographical distribution to those regions where malaria was prevnlent in Italy. The three species were Culex penicillaris, Anopheles claviger (syn. A. maculipennis), and a purported new species, Culex malariae.1 It has since been proved that only 1 In his paper in the 'Policlinico' (October 1st, 1898), Grassi writes: "In conclusione, io sono d'avviso che it Culex penicillaris e 1' Anopheles claviger o per Io meno il Culex penicillaris, fors' anche il Culex malaria, nella malaria si comportano come le zeeca nella febbre del Texas." Grassi therefore makes a misstatement in a later paper (December 1st, 1900) when he writes, " Proclamai come iudiziati due specie di culex, ma sopratutto 1'Anoplieles olaviger." It is curious that Grassi should subsequently have continued to lay stress upon the geographical coincidence having led him to the discovery of Anopheles claviger being a host of malarial parasites, for two out of three species which he for this reason supposed must be hosts were afterwards proved not to be such. He certainly considered A. claviger at first to be of quite secondary importance; we have his own words for it: " Certi casi di malaria sviluppatisi in Settembre a Locate Triulzi, nei quali gli Anopheles di certo o non puusero o soltanto rarissime volte, den unciano decisamente come trasmissore il Culex penicillaris, enorma- mente comune in tutti i luoghi malarici." (The italics are Grassi's.) It is but fair to Ross to state here that Grassi in his paper of the 1st of October refers to the experiments made by Smith and Kilborne upon Texas .