352 TRYPANOSOMA CONGOLENSE [CH. 



animals, for Laveran and Mesnil found that the average- 

 duration of the disease in this species was only two weeks and 

 invariably resulted in the death of the animal. 



Morphology of the parasite. The living parasite exhibits 

 active wriggling movements without, however, progressing 

 across the field of the microscope. The trypanosomes are often 

 attached to the leucocytes by their anterior extremities. 



The dimensions of the majority of the individuals vary 

 between lo to 13 microns in length, by i to 2 microns in 

 breadth, and the largest forms are never more than 17 microns 

 in length, a means of distinguishing this species from dimorphon. 

 In stained specimens the posterior extremity is rounded and 

 anteriorly the body of the parasite gradually tapers, the 

 protoplasm being prolonged to the extremity of the flagellum. 



The trophonucleus is situated about the middle of the 

 length of the parasite ; the kinetonucleus is very distinct and 

 is usually close to the posterior extremity. The protoplasm is 

 somewhat clear and rarely contains chromatophilous granules. 



Mode of infection. There is some little doubt as to whether 

 G. palpalis is capable of transmitting congolense, for the only 

 positive experiments with this species of tsetse-fly that have 

 been recorded up to the present are those of Roubaud, and this 

 author states that the observations were made with " T. con- 

 golense (vel dimorphon)." 



In the alimentary canal of G. palpalis Roubaud observed 

 the commencement of a development of this trypanosome 

 somewhat resembling that of T. gambiense, but the parasites all 

 disappeared by the end of the third day. 



Rodhain, van den Branden, Pons and Bequaert, found 

 that the G. morsitans in the Katanga region were naturally 

 infected with congolense. In addition an experiment was made 

 with 23 flies born in the laboratory. These were fed on an 

 infected goat and subsequently on healthy animals. After an 

 incubation period of 23 days one of the flies became infective. 

 This individual on dissection was found to present an " infec- 

 tion totale " of the ahmentary canal. The parasites in the 

 intestine were nearly all of the trypanosome type and some 

 were of the blood form. In the proboscis the hypopharyngeal 



