216 ANIMAL LIFE AND HUMAN PROGRESS 



muscid flies. Several species of Hymenoptera are parasitic 

 upon tsetse pupae, including two Mutillids and a few of the 

 smaller Chalcidoidea. Birds prey upon them to a very small 

 extent ; and recently Dr. Lamborn has given us an interesting 

 account of his observations on the capture of tsetses by dragon 

 flies. 1 



The factors concerned in the dissemination of the diseases 

 known respectively as sleeping sickness in man and trypano- 

 somiasis (nagana, etc.) in domestic stock are : 



(1) Species of Trypanosoma ; free-swimming, microscopic 

 organisms which are found chiefly in the peripheral blood. 

 These give off a toxine causing the death of the host. (Man 

 and domestic stock.) 



(2) Big game (antelopes, wart-hog, etc.). These also 

 harbour the trypanosomes, but are tolerant of their presence. 

 ; ' Big game " therefore act as the natural reservoirs for the 

 trypanosomes. 



(3) The tsetse-flies. These are also tolerant of the presence 

 of trypanosomes. A cyclical or partial development of the 

 latter takes place in the gut of the fly. Tsetses are the chief 

 and, so far as is known at present, the only vectors or dis- 

 seminators of the disease. 



(4) Man, who is generally non-tolerant and rarely survives 

 the infection. 2 Man may form an important reservoir if 

 allowed to remain in a fly -infected area. In the case of 

 nagana, etc., domestic stock takes the place of man. 



Trypanosoma gambiense is the cause of the disease in man 

 known as " Uganda Sleeping Sickness." It is supposed to 

 have been introduced from West Africa into Uganda at the 

 end of the last century. In the epidemic which ravaged the 

 native population between the years 1898 and 1906, some 

 200,000 people died of the disease. The tsetse which trans- 

 mits the disease is Glossina palpalis. 



Trypanosoma rhodesiense produces the Rhodesian and 

 Nyasaland form of sleeping sickness, which would seem to be 

 a much more virulent type of the disease in man than that 



1 Butt. Ent. Res. vol. vi. p. 552 (1915). 

 2 A chronic form of the disease occurs in West Africa. 



