680 INFECTION AND IMMUNITY. 



densation fluid, and the organisms were carried through 

 many generations. In cultures they vary greatly in size 

 (from 1 to 60 microns in length). "The existence of the 

 small forms accounts for the fact that we have repeat- 

 edly been able to infect rats with Berkefcld nitrates of 

 such cultures." It is remarkable that so many of the 

 rats which harbor the parasites appear to be perfectly 

 healthy. However, the animals not infrequently die 

 from the infection, and in some instances fairly severe 

 epidemics have been noted. The infection is found also 

 in the hamster, a European rodent, and in white rats. 

 White mice are susceptible to inoculation (Doflein). 



Trypanosoma brucei, found by Bruce in 1894 in the 

 blood of animals suffering from nagana or the tsetse-fly 

 disease in Zululand is somewhat different morphologi- 

 cally from T. lewisi, being more worm-like in form, hav- 

 ing a blunt posterior extremity, less motility and greater 

 pathogenicity. "The undulating membrane is broader 

 and more plicate, the protoplasm colors more easily and 

 more deeply" than in T. lewisi. Its length is said to 

 vary, depending on the animal which harbors it, being 

 largest in the rat and shorter and thicker in the dog. 

 Its dimensions as given by Laveran and Mesnil are 1 to 

 1.5 by 26 to 27 microns. Its structure is similar to that 

 of T. lewisi, containing a nucleus near the middle of the 

 body and a deeply staining centrosome in the posterior 

 portion in or near which the flagellum has its origin. 

 A contractile vacuole lies anterior to the centrosome. 



Natural infection (nagana) with this organism occurs 

 in horses, cattle, mules, and also in some wild animals, 

 as camels, buffaloes and hyenas. It is, however, a tropi- 

 cal disease, occurring chiefly in various parts of South 

 Africa. Nearly all animals are susceptible to artifi- 

 cial infection by the injection of diseased blood. 

 T(J t The distribution of nagana corresponds with the dis- 



tribution of the tsetse-fly, and Bruce discovered that this 

 fly, after feeding on the blood of an infected animal, 

 transfers the disease to others by biting. Horses, asses, 

 cattle and hogs were infected artificially in this way, but 

 man appears not to be susceptible. It is assumed, but 

 perhaps not definitely proved, that no other fly or insect 

 transmits the disease. Immediately after it has fed on 



