478 MITZMAIN. 



trypanosomiases is purely mechanical has been taken for granted, 

 and, in a few instances, proved by experiments. By the mechan- 

 ical method it is assumed that there is involved a direct convey- 

 ance by the insect carrier of infection either immediately or 

 in varying periods up to forty-eight hours after feeding on the 

 infected host. 



Novy, MacNeal, and Torrey,<25) referring to insects such as Stomoxys, 

 affirm that the facts, such as they are, indicate that the flies merely trans- 

 mit the surviving unaltered trypanosomes which have been taken up with 

 the blood, and that such transmission can occur only during the few hours 

 following the infective feed. 



Evans (26) cites Stomoxys as the mechanical carrier of the trypanosomes 

 of elephant surra. No experimental evidence is offered. 



Jowett(27) obtained negative results in mechanical transmission experi- 

 ments in cattle trypanosomiasis with Stomoxys fed on rats, sheep, and goats. 



Fraser and Symonds,(28) working with surra and the mechanical trans- 

 mission method with Stomoxys, were unsuccessful in five experiments. In 

 two instances 8 and 11 flies, respectively, were used. 



Gaiger(29) states that in some parts of India Stomoxys is found where 

 there is an absence of Tabanidse and the former is probably equally capable 

 of transmitting surra mechanically. 



In my experiments covering this point, an attempt has been 

 made to view the problem exhaustively from every possible angle. 

 First, the flies, transferred from their infected hosts, have been 

 permitted to complete the initial feeding prior to biting the 

 healthy animal. Second, the flies, feeding on the surra host, 

 have been interrupted within a minute, after which they were 

 transferred to a healthy animal to complete their meal. Third, 

 this interrupted feeding was repeated during several hours of 

 the day and through a period of several days. In these tests, 

 guinea pigs, monkeys, and horses have been employed. It was 

 found that the species of susceptible mammal used made no 

 difference in the results of the experiments. The use of animals 

 other than the natural hosts of Stomoxys has been criticized 

 by several workers. A limited experience convinces me, so far 

 as many negative results can convince, that the reaction to bit- 

 ing of infected flies is similar in all the hosts cited. 



The experiments were carried on with animals in a large cage, 

 or in a glass jar, or in the open with the host immobilized. 

 In the first case the insects were placed in the cage or in the jar 

 and permitted to bite at will. By the second method they were 

 applied in a large bottle to the tail of the animal, and also in- 

 dividually in test tubes. Both wild flies and laboratory-bred flies 

 were used, and in each case this condition is stated. 



In all of the experiments reported upon in this paper the 



