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Rh through the microscope, the blood seems to seethe and quiver with the rapidly moving parasites. Specimens are easily procured by snipping off with scissors the tip of the rat's tail and dabbing the cut surface on the slip.

T. lewisi measures, on an average, including the flagellum, 24-25 μ by 1.5 μ; the posterior extremity is said to be more pointed than in the other known mammalian trypanosomes. The nucleus is situated in the anterior half or third of the body; the cytoplasm is very clear and free from granules. There is evidence that it is conveyed from rat to rat by the rat-louse and rat-fleas, which are now known to be its true alternative host. It is not, apparently, transmitted by the salivary glands of the insect, but multiplies in the hindgut of the flea, and, after assuming various crithidial forms, escapes in the excreta, and is thus inoculated into the wound made by the flea's proboscis.

In experimental rats it has been found possible to transmit infection to other rats through the unbroken skin by rubbing on cultures of this trypanosome.

It is generally held that T. lewisi is non-pathogenic. Certainly, infected rats usually exhibit a remarkable tolerance towards this parasite, but occasionally they do sicken and die.

The fact that the rat is susceptible to laboratory inoculation with the trypanosomes of man and cattle indicates the possibility of finding other species of trypanosomes in the blood of wild rats.

T. evansi (Steel, 1885); length, 22-30 μ; breadth, 1-2.5 μ. This parasite was discovered in 1880 by Griffith Evans in the Punjab, in the blood of horses suffering from surra, a disease which the natives of India ascribe to the bite of certain horse-flies (Tabaindae). T. evansi is not limited to horses and mules, but attacks also camels, elephants, buffaloes, and dogs. Experimentally it has been transferred to monkeys, rabbits, rats, mice, and guineapigs ; in nature, infection of dogs by feeding on animals dead of surra has frequently been observed. It has a very wide distribution in Southern Asia and in Malaya. It has been recently imported into Mauritius and the Philippines. We have no positive knowledge as to the definitive host or hosts of this trypanosome. Various blood-sucking flies belonging to the genera Stomoxys, Haematobia, and Tabanus have been incriminated. In Mauritius the epidemic is thought to have been spread by Stomoxys nigra.

The disease known as "Mbori," occurring among drome-daries coming from the Sahara into the Soudan (Timbuctoo, etc.), which is apparently also conveyed by a tabanus, is considered both by Vallee and Panisset, and by Laveran and Mesnil, to be a milder form of surra, the parasite which causes it being a "variety" of T. evansi.

T. brucei (T.pecaudi) (Plimmer and Bradford, 1899); length, 28-30 μ; breadth, 1.5-2.5 μ. The anterior extremity is usually bluntly rounded. The cytoplasm often contains in the posterior half large, deeply staining granules. This parasite