532 FAMILY: TRYPANOSOMID^ 



that trypanosomes {T. hrucei) had been seen by Bruce (1897) in the 

 proboscis up to forty-six hours after feeding, the conclusion was arrived at 

 that the transmission was a mechanical one. The experiments carried out 

 by Bruce, Nabarro, and Greig (1903), however, indicated that a cyclic 

 development in the fly was not excluded, for freshly caught flies were 

 shown to infect monkeys. It was shown by Minchin (1908) and others 

 that in mechanical transmission it was not possible for a fly to infect more 

 than one animal, the proboscis being apparently purged of trypanosomes 

 at the first feed. Minchin, Gray, and Tulloch (1906), and Minchin (1908), 

 working with single flies {G. palpalis), transmitted T. gamhiense nine times 

 out of ten by the method of interrupted feeding, by which the flies were 

 allowed to commence their feed on an infected animal and to complete it 

 on a healthy one. Bruce et at. (1910/), by using laboratory bred flies, 

 proved that mechanical transmission of T. gatnbiense by G. palpalis could 

 take place within two hours of feeding. It was recognized that in the 

 earlier experiments noted above, when wild flies were used, what had been 

 regarded as mechanical transmission after forty-eight hours was probably 

 due to the flies having already been infected in nature. 



Much confusion regarding the behaviour of trypanosomes in the flies 

 was at flrst caused by Herpetotnonas grayi, which was not distinguished 

 from T. gamhiense (Figs. 173 and 220). Minchin, Gray, and Tulloch (1906) 

 first showed that this flagellate was distinct from T. gamhiense, a fact 

 which was recognized later by Novy (1906), who examined films sent him 

 by Gray. After H. grayi had been recognized, the behaviour of T. gam- 

 hiense in G. palpalis was studied by Minchin, Gray, and Tulloch (1906), 

 who found that the ingested trypanosomes disappeared entirely from the 

 gut of the fly in four days. This led Minchin (1908) to express the view 

 that T. gamhiense in Uganda was transmitted by G. palpalis in a purely 

 mechanical manner; though influenced by the work of Koch (1905) and 

 Stuhlmann (1907), chiefly on T. hrucei, he still held that, given the proper 

 conditions and the proper fly, a true cyclic development would be found 

 to take place. Koch (1905) noted that a fluid free from red blood-corpuscles 

 and containing large numbers of trypanosomes could be expressed from 

 the proboscis of wihl tsetse flies, G. fusca (? G. hrevipalpis), G. morsitans, 

 and G. palpalis. From what is now known, these trypanosomes, which 

 were of the vertebrate blood type, were undoubtedly the metacyclic 

 infective forms. It was probably these forms which Gray and Tulloch 

 (1905) found in the salivary glands of a fly. Stuhlmann (1907) confirmed 

 Koch's observations, and also noted long narrow forms in the proven- 

 triculus. He found that from 3 to 14 per cent, of wild tsetse flies, G. fusca 

 (? G. hrevipalpis), had trypanosomes in the proboscis. Roubaud (1908) 

 also obtained trypanosomes from the proboscis of wild flies. Bruce 



