172 THE KINGDOM OF MAN 



that the wings, when the insect is at rest, are parallel to 

 one another, and slightly over-lap in the middle line, 

 instead being to a small extent divergent at their free 

 extremities. The bite, like that of all flies, is rather 

 a stab than a bite, and is effected by a beak-like process 

 of the head, the blood of the animal pricked in this way 

 being drawn into the fly's mouth by a sucking action of 

 the gullet. The tsetze flies appear to be especially greedy 

 and are said to gorge themselves to such an extent that 

 the blood taken in from one animal overflows the gullet, 

 and so contaminates the wound inflicted by the fly on the 

 next animal it visits. It is at the present moment 

 assumed very generally that this is the way in which 



Tsetze flies Glossina morsitans 

 magnified two diameters. This is 

 the ' fly ' of the Nagana or horse and 

 cattle disease of South Africa. The 

 Glossina palpalis, which carries the 

 Trypanosoma Gambiense causing sleep- 

 ing sickness, is very closely similar 

 to it in appearance. 



infection is produced. But it is not at all improbable 

 that the trypanosome undergoes some kind of multiplica- 

 tion and change of form when sucked into the tsetze fly 

 as happens in the case of the malaria parasite when 

 swallowed by the Anopheles gnat, No such change has 

 yet been discovered in regard to the trypanosome of 

 sleeping sickness : but it cannot be said that the matter 

 has been exhaustively studied, or that a negative conclu- 

 sion is justified. 2 



2 Professor Minchin investigated this subject during 1 905 in Uganda 

 whither he went on behalf of the Tropical Diseases Committee of the 

 Royal Society. He did not discover anything corresponding to the 

 development of the malarial parasite in the gnat, but his investigations 

 are not yet brought to a conclusion (December, 1906), 



