512 



FAMILY: TRYPANOSOMIDiE 



several species of trypanosome, and this fact led Kleine and Fischer (1912) 

 to express the view that any species of tsetse fly would probably be able 

 to transmit any of the pathogenic trypanosomes with which it was in 

 contact. The flies, which inject the trypanosomes when they bite, become 

 infective after the trypanosome has passed through a definite cycle of 

 development, terminating in the production of metacyclic trypanosomes. 

 The cycle requires about twenty days for its completion. In an ingenious 



experiment, Rodhain, Pons, 

 Vandenbranden, and Bequa^rt 

 (1912c), induced G. morsitans 

 infected with T. brucei to feed 

 through a membrane covering 

 a tube in which citrated blood 

 was contained. After a fly had 

 fed, the number of trypanosomes 

 in a portion of the fluid were 

 counted, and it was estimated 

 that a single infected fly was able 

 to inject 1,562 metacyclic try- 

 panosomes while feeding. 



It has been clearly demon- 

 strated that a purely mechanical 

 transmission may also occur by 

 the fly contaminating the wound 

 it inflicts with infective blood 

 which it has recently taken into 

 its proboscis from another host. 

 Duke (1919) believes that the 

 ejndemic of sleeping sickness 

 which swept over Uganda was 

 largely due to mechanical 

 transmission of infection from 

 man to man by Glossina pal- 

 palis. This view is further 

 developed by Duke (1921, 1923, 

 1923r/.), who concludes that wherever human trypanosomiasis occurs in 

 epidemic form in Africa, the transmission is a mechanical one. Certain 

 experiments made by him (1923a,) are held to prove that when the human 

 trypanosome is passed directly from monkey to monkey by direct 

 inoculation of blood, it eventually loses its power of passing through the 

 complete cycle in the tsetse fly, and he assumes that a similar change may 

 occur after prolonged mechanical transmission from man to man. 



Fig. 216. — Glossina morsitans ( 9 ) Dorsal 

 AND Side Views (x 4-5). (After 

 Xewstead, 1924.) 



