534 FAMILY: TRYPANOSOMID^ 



Pons, Vandenbranden, and Bequa^rt (19126) succeeded in transmitting 

 T. gambiense by means of laboratory bred G. morsitans fed on infected 

 monkeys. Kleine and Fischer (1912) also succeeded in a similar experi- 

 ment, as did Bruce et al. (1915). Taute (1911) fed G. morsitans on a 

 monkey which had been infected from a man. These flies kter infected 

 healthy monkeys. Lloyd and Johnson (1924), working in North Nigeria, 

 have transmitted T. gambiense by means of G. tachinoides , in which a 

 complete development of the trypanosomes occurred. It appears that 

 in certain areas this fly is responsible for the spread of sleeping sickness. 

 These instances can only be regarded as exceptions to the general rule 

 that T. gambiense is transmitted in nature by G. 'palpalis. 



T. gambiense may also be transmitted in a mechanical manner by 

 mosquitoes and other biting flies. Thus, Heckenroth and Blanchard 

 (1913) showed that mosquitoes {Mansonia uniforinis) could infect guinea- 

 pigs within twenty-four hours of feeding on an infected animal, while 

 Minchin, Gray, and Tulloch (1906) were successful with Stomoxys which 

 had partially fed on an infected animal and had completed its feed on a 

 healthy one. In the latter case, the trypanosome transmitted was possibly 

 T. brucei, and not T. gambiense. Duke (1919, 1923) has come to the 

 conclusion that mechanical transmission of a virulent strain of T. gam- 

 biense from man to man was largely responsible for the spread of sleeping 

 sickness through Uganda from 1900 to 1910. He believes that when 

 human trypanosomiasis occurs in epidemic form, mechanical transmission 

 is responsible for the rapid spread of the disease, while transmission 

 associated with the cycle of development in the fly maintains the disease 

 in endemic form. 



Cycle in the Tsetse Fly.— The main outline of the development of 

 T. gambiense in G. palpalis (Fig. 223) was described by Bruce et al. (1911f7). 

 It was studied in greater detail by Robertson (1913), whose account is 

 follov/ed here. 



When a fly hatched from the pupa ingests blood and trypanosomes 

 from an infected animal, one of several alternatives may occur. 



1. The trypanosomes may be destroyed and disappear during the 

 fifty to seventy-two hours during which the blood is being digested. 



1. Trypanosome of the blood-stream. 2. Division of blood form. 



3. Tryijanosome in mid-gut thirty-six to forty-eight hours after feeding. 

 4-6. Tryimnosome in hind-gut third or fourth day of cycle. 



7. Trypanosome in mid-gut on fifth day. 



8. Large multiple form (delayed division) sixth day. 

 9-11. Trypanosomes in gut twelfth to twentieth day. 



12-13. Slender proventricular types — final form of gut development. 



14-15. Form newly arrived in salivary glands. 



16-20. Typical salivary gland— crithidia forms. 



21-23. Final trypanosome types in salivary glands (metacj'clic trypanosomes). 



