XVIII] MODE OF INFECTION 337 



Bouffard found that out of 224 tsetse that ingested T. cazalboui, 

 no less than 38-8 per cent, became infected. In Uganda, 

 Bruce and his collaborators found that under similar circum- 

 stances about 20 per cent, of palpalis shewed a development 

 of trypanosomes in the proboscis. 



The effect of climate on the development of this trypanosome 

 in the intermediate host is well shewn by the results of Bouet 

 and Roubaud in Upper Dahomey and the Nigerian Sudan, 

 during the dry season. In these regions only two species of 

 Glossina, namely tachinoides and morsitans, were found during 

 the summer, all palpalis having disappeared as a result of the 

 dry weather. Experiments were undertaken to determine 

 which of these species was most liable to infection with T. 

 cazalboui. Although in Middle Dahomey tachinoides was as 

 efficient a carrier as palpalis, in the dry regions of Upper 

 Dahomey and the Nigerian Sudan the same species was only 

 infected with great difficulty, the authors concluding that during 

 the dry season, at any rate, G. tachinoides of the regions between 

 12 and 13 north latitude is unable, or only slightly able, to 

 infect with the endemic viruses, or those which it is able to 

 transmit outside these areas. On the other hand, about 50 per 

 cent, of wild morsitans captured at random were found to be 

 infected ; the development of the trypanosome in this species, 

 however, is somewhat slower than in palpalis, tachinoides and 

 longipalpis, respectively. In the Katanga district the mem- 

 bers of the Belgian Sleeping Sickness Expedition (1912) 

 found an equally large percentage of morsitans infected with 

 cazalboui. 



The development of the trypanosome in the tsetse-fly is 

 restricted to the proboscis, the flagellates never multiplying in 

 any other part of the alimentary canal. Palpalis, tachinoides, 

 and longipalpis, become infective about six to seven days 

 after an infecting feed, whilst in the case of morsitans this 

 developmental period is prolonged to eight to ten days. 



In Uganda, the development of T. cazalboui is much slower 

 than in the West African Provinces, for the members of the 

 Sleeping Sickness Commission at Mpumu, found that the non- 

 infective period varied from n to 35 days. 



H. B. F. 22 



