200 THE HAEMOFLAGELLATES 



being fed, experiments being carried out up to an interval of twenty-two 

 days. An additional and significant fact remarked upon by them is that 

 only the first animal which the experimental fly was allowed to stab 

 became infected ; if the insect was removed before its meal was completed 

 and immediately placed on another animal, this latter did not become 

 infected. That is to say, after a fly had been allowed to, as it were, clean 

 its proboscis from the Trypanosomes remaining in it since its previous 

 meal (on an infected animal), it was no longer infectious. 



These facts make it certain that Trypanosomes can be and are 

 conveyed by Tsetse-flies in a purely direct and mechanical manner ; 

 and so far as T. gambiense and sleeping-sickness in Uganda are 

 concerned, it is probable that their spread, through the agency of 

 G. palpalis, has been largely if not entirely in this way. But this 

 does not by any means end the matter. 



Minchin, Gray, and Tulloch bring forward observations which 

 point to a commencing cycle of development of T. gambiense 1 in the 

 fly. Up to forty-eight hours the Trypanosomes present in the 

 stomach of an infected fly are markedly differentiated into two 

 types, which probably represent sexual forms. After forty-eight 

 hours a type of more indifferent character makes its appearance, 

 which usually becomes scanty with lapse of time, till at ninety-six 

 hours scarcely a Trypanosome can be found. It is interesting to 

 note that during this interval the parasites steadily increase in 

 size. Coming next to Koch's recent investigations on behalf of 

 the German Sleeping- Sickness Commission, a very important 

 observation is recorded (29). A species of Glossina, distinct from 

 G. palpalis, namely, G. fusca, was bred in captivity ; the individuals 

 born and reared under these conditions were regarded as certainly 

 free from Trypanosomes. 2 Several of these flies were fed on rats 

 infected with T. gambiense. They were examined from ten to 

 twelve days later, and after this long interval were found to be 

 infected with those parasites. Moreover, individuals of another 

 Tsetse-fly, G. tachinoides, similarly fed, were also found to contain 

 T. gambiense after the same lengthy interval. 



Still more recently Stuhlmann (80), in his description of G. 

 fusca, has published some extremely interesting notes on the relation 

 of T. brucii to this fly. Using reared flies, considered to be certainly 

 free from infection, Stuhlmann was able to infect about 80 to 90 



1 The case of T. gambiense in Glos&ina palpalis is unfortunately complicated by 

 the occurrence in the same species of fly of other Trypanosomes, distinguished by 

 Novy (61) as " fly-Trypanosomes." One of these, T. grayi, at any rate is entirely 

 different from T. gambiense ; and it is highly probable that some of the observers (e.g. 

 Gray and Tulloch [23], Koch [28]), who first described what they regarded as 

 developmental phases of T. gambiense, were dealing in reality with T. grayi. 



' 2 This is on the assumption, of course, that the parasites were not inherited ; but 

 most authorities seem to be agreed that hereditary transmission of Trypanosomes by 

 Tsetse-flies does not take place. 



