It was clearly shown from these investigations that the disease was due to a flagellated protozoon similar to that previously described by Evans as existing in the Surra of India. This organism was subsequently designated by Plimmer and Bradford as Trypanosoma brucei. Bruce further demonstrated that the disease was spread by the bite of infected tsetse flies. The trypanosomes were found alive in the insects' proboscides up to forty-six hours after the flies had sucked infected blood. Motile parasites were still found in the flies' stomachs after 118 hours, but after 140 hours their stomachs were empty, and apparently dead parasites were found in the excreta. When contaminated flies were kept for twelve to forty-eight hours before they were allowed to bite healthy dogs, these only sickened on the thirty-second to thirty-eighth day, instead of after two weeks, as is usually the case. Nagana blood when removed aseptically produced the disease when kept for four days, but not after seven days. The blood when dried on threads produced infection after twenty-four hours in only one of three animals. Kanthack, Durham, and Blandford in 1898 published the results of their studies on the trypanosome of Nagana. The material for this study was obtained from the blood of an infected dog brought to England from Zululand in 1896. We may say in passing that all of the subsequent investigations made in Europe, except that of Martini, were made with trypanosomes derived from this source. The observers mentioned found that in drawn blood, or in serous fluids, the hematozoa soon became motionless. This may occur rapidly, for instance in twenty minutes, but generally some motile specimens may be found after two to three days; sometimes, indeed, after as long as five or six days. Within a cadaver the blood and organs became non-infective in about twenty-four hours. They made numerous attempts at cultivation in normal blood, but while they observed the formation of tangles or agglutination masses, and, eventually, degeneration forms represented by masses of spherules, they failed to obtain any evidence of multiplication.

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Danilewsky examined more than 300 birds, but gave no details as to the frequency and number of the trypanosomes found by him. They were met with in the blood of owls, rollers, lannerets, etc., and the number was said to vary with the individuals and the season. In one case they were found in young rollers (Coracias garula) but three or four days old. They were also found in young featherless lannerets. He observed only one form of trypanosome which to him corresponded perfectly with the Tr. fusiforme (piscium) of fish. According to the size he divided this into Tr. majus and Tr. minus. The length of the latter, not counting the flagellum, varied from 18-22/'; while that of the former was 45-60/,. The young forms (9-10/'), arising by segmentation, he designated as trypanomonas. Whereas in the heart-blood but one or two trypanosomes could be found, and then only with difficulty, in the red marrow of bones they were detected in large numbers. It would seem as if the red marrow was the principal place where these organisms are found. Although Danilewsky designated the trypanosomes by several names, such as 'I