in the blood of animals affected by this disease, and to bring forward my reasons for considering it to be the proximate exciting cause of the disease. For the present I shall call it the Haematozoon or Blood Parasite of Fly disease, although in all probability on further knowledge it will be found to be identical with the haematozoon of Surra, which is called Trypanosoma Evansi or at least a species belonging to that genus...He also made accurate identification characters of the parasite as unique organisms:[Under a microscope] can be seen transparent elongated bodies in active movement, wriggling about like tiny snakes and swimming from corpuscle to corpuscle, which they seem to seize upon and worry. They appear to be about a quarter of the diameter of a Red Blood Corpuscle in thickness, and 2 or 3 times the diameter of a corpuscle in length. They are pointed or somewhat blunt at one end, and the other extremity is seen to be prolonged into a very fine lash, which is in constant whip-like motion. Running along the cylindrical body between the two extremities can be seen a transparent delicate longitudinal membrane or fin [later named undulating membrane] which is also constantly in wave-like motion... These parasites evidently belong to a very low form of animal life, namely the infusoria, and simply consist of a small mass of protoplasm surrounded by a limiting membrane, and without any differentiation of structure, except in so far as the membrane is prolonged to form the longitudinal fin and flagellum.He performed several experiments on different animals as to how the parasite was transmitted. He found that the tsetse fly (Glossina morsitans), which was common in the region, could carry the live parasites from feeding on blood of the animals. He established that "the Tsetse Fly plays a most important part in the propagation of the disease", but was unable show that the flies could actually transmit the disease. He explained:I have not been able exactly to prove the part which the Tsetse Fly plays in the causation or production of the Fly Disease, I think it well to begin with a consideration of the Fly itself, not only on account of its historical value, but also because I am at present of opinion that the Tsetse Fly does play some part, and perhaps no inconsiderable part, in the propagation of the disease. Be it at