METHOD OF PROPAGATION 561 



recover from nagana. Whether such animals which have recovered 

 ever become entirely free from trypanosomes or whether they retain 

 them in small numbers without detriment to themselves is a different 

 question. The author during his stay in the Philippine Islands 

 repeatedly examined microscopically the blood of a Government 

 herd of about forty carabaos. These animals had gone through an 

 attack of surra, had apparently recovered from it, were in good 

 flesh, and strong and able to work. Examinations were frequently 

 negative. From time to time, however, a few trypanosomes were 

 found in the blood, and undoubtedly non-immune animals may be 

 infected from apparent immunes harboring such trypanosomes in 

 their blood, without detriment to themselves. This is an important 

 matter from the standpoint of prophylaxis. 



FIG. 194 



A tsetse fly (Glossina longipennis, Corti, from Somaliland) in resting attitude, showing 

 position of wings. X 3^. 







Tsetse flies infected with trypanosomes are dangerous for a short 

 time only. It has been shown by Bruce and others that these insects 

 after having fed on an infected animal can only spread the disease 

 within forty-eight hours. Carnivora may also contract nagana by 

 devouring the flesh and blood of infected animals. When carnivora 

 become infected in this manner it is very probable that this is brought 

 about through injuries in the buccal mucous membrane. Musgrave 

 and Clegg, who experimented with horses, dogs, goats, rabbits, guinea- 

 pigs, monkeys, and cats, have shown in numerous experiments that 

 feeding trypanosoma-infected blood or other material only lead to 

 an infection in the presence of an injury to the mucosa of the gastro- 

 intestinal tract. 



The question presents itself whether trypanosomes in the body of 

 their intermediary host (the tsetse fly) undergo a cycle of life changes 

 36 



