330 TRYPANOSOMA BRUCEI [CH. 



are frequently infected with the trypanosome. These wild 

 animals, however, seem to have become immune against the 

 disease, for they may harbour the parasite in the blood for long 

 periods without suffering from any apparent ill-effects. 



The wild game, therefore, serves as a reservoir for the 

 infection, as in the case of T. gambiense, and thus, in nature, 

 generally a large proportion of G. morsitans and pallidipes are 

 infected with T. brucei. 



The morphology of the parasite. In the living state, T. 

 brucei displays active movements, as its undulating membrane 

 is well developed. Its translatory powers, however, are far 

 inferior to those of T. cazalboui and it rarely moves out of the 

 field of the microscope. 



The dimensions of the parasite according to Bruce vary 

 from 15 to 34 microns in length. Moreover the species is 

 somewhat dimorphic, the short stumpy forms measuring from 

 2 to 5 microns in diameter and the elongated forms only about 

 1-5 microns in diameter. According to Laveran and Mesnil 

 the average length of the parasite in horses is 28 to 33 microns 

 and in dogs and the smaller rodents 26 to 27 microns. 



In stained specimens the protoplasm usually contains 

 numerous granules, especially in the anterior region of the 

 body. The kinetonucleus is distinct, and is generally situated 

 near the posterior extremity, especially in the shorter forms. 

 The undulating membrane is much folded and the flagellum 

 usually becomes free at its anterior extremity. 



The trypanosome multiplies by simple longitudinal division. 



Mode of infection. The experiments of Bruce in Zululand 

 shewed that Glossina pallidipes and morsitans were able to 

 transmit T. brucei, but the exact mode of infection remained 

 unknown until Kleine's observations were published. 



In 1909, Kleine shewed experimentally that G. palpalis is 

 able to transmit this disease, and in addition that the trypano- 

 some underwent a cyclical development in its invertebrate host. 

 The account of the first experiment in which this important 

 discovery was made is as follows : 



Since nagana did not exist in the Kirugu region (in German 

 East Africa) some sheep and a mule were brought from a place 



