XVIII] MORPHOLOGY AND TRANSMISSION 333 



infection is invariably fatal. In these animals the parasites 

 are numerous in the late stages of the disease. 



Morphology of the parasite. In the hving state the move- 

 ments of the trypanosome are very active. In stained 

 preparations two types can be distinguished, namely, long thin 

 forms and short broad forms. 



The long thin forms measure about 25 to 35 microns in 

 length by about 1-5 microns in breadth. The posterior ex- 

 tremity is drawn out to a point. The undulating membrane 

 is very narrow and the fiagellum anteriorly is free for about 

 one-quarter of its length. The elongate trophonucleus is 

 situated about the middle of the body and the kinetonucleus 

 is some distance away from the posterior extremity. The 

 cytoplasm is free from granules. 



The short forms measure from 14 to 20 microns in length 

 by 3 to 4 microns in breadth. They are stumpy in ap- 

 pearance and the undulating membrane is very well developed ; 

 there is no free flagehum. The trophonucleus is large and round 

 and the kinetonucleus is situated almost at the posterior 

 extremity. The cytoplasm often contains numerous granules. 

 In the Bahr el Ghazal strain, Wenyon found many forms in 

 which the kinetonucleus was near to the trophonucleus and a 

 few in which the latter was at the posterior end of the body. 



Both the long and short forms multiply by ordinary longi- 

 tudinal division. 



Mode of infection. T. pecaudi is transmitted mainly if not 

 entirely by tsetse-flies. The experiments of Bouet and Roubaud 

 in Dahomey have shewn that, in this region, G. longipalpis 

 is the most favourable intermediate host, but tachinoides, 

 palpalis and morsitans, can also carry the disease. 



These two authors found that the longipalpis caught on the 

 banks of the Oueme River, in the neighbourhood of Agouagon, 

 were heavily infected with T. pecaudi. Thus batches of 45 

 flies and upwards, almost invariably produced infections of 

 pecaudi when fed on susceptible animals. On the other hand, 

 several hundred palpalis and tachinoides captured in the same 

 area and similarly fed on susceptible animals never produced 

 any infection, so it is evident from the epidemiological point 



