in which he discovered a parasite in the blood during life. At first Evans believed it to be a spirillum, but subsequently came to the conclusion that it was a much higher organism. His observations have an important bearing on the question of the parasites in malaria. In 1885, Veterinary-Surgeon Steel published "An Investigation into an Obscure and Fatal Disease among Transport Mules in British Burma," which also proved to besurra. A careful clinical investigation of the disease led to the conclusion that it was a true relapsing fever, very similar to recurrent fever of man. Steel found the parasite described by Evans in all cases, and determined that it appeared as the temperature rose and disappeared in the intervals between the paroxysms. He regarded it as a true spirillum, and named it Spirochceta Evansi. Both Steel and Evans found the disease readily communicable to dogs, horses, and mules, either by inoculation or by ingestion. Recently, on the return of Dr. Evans from India, he placed material from thesurradisease in the hands of Dr. Crookshank, who has made an elaborate report,[1] confirming Dr. Evans's view that the organism is not a spirillum, and states that the parasite is morphologically identical with the hæmatozoa described by Mitrophanow in the carp and mud-fish. In 1879, Lewis[2] described certain parasites in the blood of rats in India; and, again, in 1884,[3] he more fully discussed the question, and spoke of the identity of the organism with that found in the surra disease. Crookshank, in the paper just mentioned, gives the results of his investigations on the blood of European rats, 25 per cent of which he finds infested with Lewis's parasite. It is a flagellate organism, with an undulating fin-like membrane, and is highly polymorphic. Crookshank has distinguished "globose, angular, non-filamentous, bi-flagellate, semi-circular, and disc forms;" the latter represent the encysted stage. This organism is believed to be morphologically identical with the surra parasite and with Mitrophanow's hæmatozoa.
In the Biologisches Centralblatt, 1885, Professor Danielewsky, of Charkoff, makes an important contribution to the subject. He states that Trypanosoma, the well known flagellate organism of frog's blood is polymorphic, and occurs in an amœboid form, and also produces spores; and, further, he has found in the red blood-corpuscles of birds a pigmented protoplasmic body, which subsequently appears in the plasma as a pigmented flagellate organism. In a later communication,[4] he suggests the identity of the pathogenic blood parasites of man with the hæmatozoa of healthy animals, and refers specially to the similarity of the forms which he has found in birds to certain of those described by Laveran in malaria.
With this information, we are in a better position to discuss the relation of the forms described to each other, and the zoological position of the organism. It is evidently closely allied to the hæmatozoa just spoken of, and the facts which we know of their life-history enable us to assert, with greater confidence, that we are here dealing with the varieties of a highly polymorphic species, and not with two or three different organisms. The flagellate form is doubtless the adult condition; and it is interesting to note, in contrast to the hæmatoaoza of the rat and of the surra disease, the comparative infrequency of its occurrence. Laveran met with it ninety-two times in four hundred and thirty-two cases, and Councilman eleven times in eighty cases. The steps in development remain to be worked out. It seems clear, however, that the pigmented amœboid form may become transformed into a sporocyst (represented by the rosette form and its changes), or into an encysted body (resting form), the crescent. The gaps in our knowledge relate specially to the form and manner of entrance of the parasite in to the red corpuscle. Do the solid particles contained in the vacuoles (Figs. 5 and 6) represent the earliest stage? I think it highly probable that they do, and that they, with the hyaline unpigmented bodies, are the immature forms. The spore-like structures which result from the segmentation of the rosette form do not resemble the small solid bodies seen in the red corpuscles, but are rather like the tiny free pigmented forms which, in some cases, were abundant in the plasma. Of the latter, various sizes are found, and it is possible that from them the adult flagellate bodies arise. Golgi suggests that the spores, resulting from the segmentation, pass to the spleen, and there attack the red corpuscles, in which they develop into the amœboid forms. As at present the data are not available for a final decision, a further consideration of these points need not detain us. There is sufficient evidence to show that the various forms are only phases in the life-history of one of the flagellate protozoa, belonging to the order Flagellata-Pantostomata. Mitrophanow suggests a new genus, Hæmatomonas, to include the monad hæmatozoa; but Crookshank, who has carefully worked out the affinities of the parasites of the rat, the fish, and the surra disease, has referred them to the genus Trichomonas. The organism here described has not, however, the characteristic marks of a trichemonas; for it lacks the undulating fringe on one side and the caudal filament. Nor does it agree with the features of a Cercomonas; so that, meanwhile, until the true affinities are determined by an expert, its proper place seems to be the genus Hæmatomonas of Mitrophanow, which conveniently includes all monads parasitic in the blood. Thus: genus, Hæmatomonas; species, Hæmatomonas malariæ. Definition: Body plastic, ovoid, or globose, no differentiation of protoplasm, which contains pigment grains; flagella variable from one to four. Highly polymorphic, occurring in (1) amœboid form; (2) crescents, encysted form; (3) sporocysts; (4) circular, free, pigmented bodies. The name designates the natural affinities of the parasite, its habitat, and the conditions under which it occurs, on which grounds it seems preferable to that of Plasmodium malariæ, suggested by Marchiafava and Celli.
Relation of the Parasites to the Disease.—The same difficulty meets us here as in so many affection is in which micro-organisms have been found: Are they pathogenic, or are they merely associated with the disease, which in some way furnishes conditions favourable to their growth? As evidence of their pathogenic nature may be urged, with Laveran, the constancy of their presence, their absence, in other individuals in malarial regions, the destructive influence upon the blood-corpuscles, and their abundance in the graver forms of the disease. But even these considerations, weighty as they may appear, will not carry conviction to all, in the absence of experimental demonstration such as can be afforded in the case of certain pathogenic schizomycetes. Attempts to isolate and grow these hæmatozoa outside the body have failed. Marchiafava and Celli have shown that the inoculation of healthy persons with blood taken from a case of malaria is followed inavariable time by genuine ague paroxysms, in which the blood contains the parasites; but in regions where malaria is prevalent such experiments are not wholly free from objections. A series of negative observations on undoubted cases of malaria would be convincing. I lay no special stress on the three cases in which I did not find the parasites, as the patients were not followed from day to day with the accuracy necessary to give any value to the observations. It must be borne in mind that hæmatozoa are not uncommon in animals, and, as in the rat, do not appear to interfere seriously with the health of their hosts. Under these circumstances, the association of a specific form with a definite disease in an animal makes it all the more probable that the species is pathogenic. A further study of the surra disease is, particularly, to be desired with the new light which Evans and Crookshank have thrown upon it. the conditions under which the disease occurs, combined with its paroxysmal character, are so similar to those of malaria, that a full explanation of its pathogeny would have a very direct bearing upon the present question.
To my mind, two facts in connection with these hæmatozoa point significantly to their etiological association with malaria. First, the positive anatomical changes which can be directly traced to their action, changes upon which one at least of the most marked symptoms of the disease depends; I refer to the destruction of the red blood-corpuscles, which can be followed in all its stages, and is as well-defined an alteration of tissue brought about by a parasite, as any of which we know. The second fact is the action of quinine upon the parasites. The simultaneous disapearance of the symptoms of the disease and the hæmatozoa suggest that the specific influence of the medicine is upon the parasites, though it may be urged that the quinine, while curing the disease, simply removes the conditions which permit of their growth in the blood.
Practical Cocirations.—An interesting practical point is the diagnostic value of the presence of these bodies. There were six or eight cases in which the examination of the blood proved of great service in determining the existence of malaria. Some of these are worth mentioning. One of the first was a man aged 37, who had been under observation on three or four occasions with anæmia and an enlarged spleen. He had had three attacks of hæmatemesis. There was no history of malaria, and, from the gravity of the case, I was led to regard it as one of severe splenic anæmia. On his fourth visit, however, a careful examination of the blood revealed the presence of the parasites, and I gave, in consequence, a more favourable prognosis in the case, which has since been justified. In an instance of pernicious malaria admitted to the Philadelphia Hospital, under the care of my colleague, Dr. J. H. Musser, the diagnosis rested on the discovery in the blood of the characteristic changes in the corpuscles. To a third case, No. 41, I have already referred, and there were four or five other instances of chronic malaria in which the nature of the dis-
