508 MITZMAIN. 



of infected tsetse flies are capable, or are alone capable, of transmitting 

 the trypanosomes." {Tr. gambiense.) 



Fraser and Duke (53) give detailed results in feeding hundreds of labo- 

 ratory-bred Glossina thirty days upon healthy monkeys to determine if a 

 hereditary transmission of Tr. gambiense existed. Only negative results 

 were obtained. 



Kleine and Taute(54) used thousands of tsetse flies bred from pupae 

 without encountering a single instance of hereditary transmission of the 

 sleeping-sickness trypanosome. They view with skepticism the finding of 

 trypanosomes in the eggs of infected flies. 



Kleine (65) found that none of the experiments with Gl. morsitans and 

 Tr. gambiense supported the theory of hereditary transmission of the 

 trypanosome. Hundreds of flies were used. 



Bruce and others, (49) in experiments with laboratory-bred Glossina and 

 Bleeping sickness, obtained no evidence of hereditary transmission in the 

 use of several hundreds of flies. 



Baldrey(43) expresses a belief in the theory of transmission by heredity. 

 His observations relate to Stomoxys, Tabanidae, and surra. 



Minchin writes that, so far as it is permissible to draw general conclu- 

 sions from experiments which yield negative results, it appears that 

 trjrpanosomes are not transmitted from parent to offspring in insect carriers. 

 The experiments referred to were carried on in 1911 with fleas and Trypa- 

 nosoma lewisi, by Minchin and Thomson. These authors sum up their ex- 

 perience thus: Experiments on a large scale had been done to see if trans- 

 mission can take place hereditarily in the flea, that is to say, whether the 

 offspring of the infected flea themselves may be infected. These were 

 continued for some months, but have always been negative. 



Aside from the biological significance of hereditary transmis- 

 sion, there is involved a practical problem for the laboratory 

 worker. If pathogenic trypanosomes were inherited, the same 

 objection for employing wild flies would hold for laboratory-bred 

 flies whose parents were wild. Under these circumstances the 

 newly emerged laboratory-bred flies would need to be proved 

 surra-free prior to their experimental use. 



In the present series of experiments the aim was, first, to test 

 the possibility of the transmission of surra from fly to fly through 

 the egg to the new generation, and, second, to simulate the 

 possibility of conveyance of the trypanosomes through the imago 

 of flies, the larvae of which were fed on infected material. 



In the first of these experiments the flies used were the 

 progeny of flies fed, previous to egg laying, on surra-infected 

 guinea pigs for periods of from three to five days. The eggs 

 were laid from February 27 to March 15, 1912; within a day 

 after emerging the new flies were fed on a healthy guinea pig. 

 Daily additions to the number of flies fed were made as fast as 

 they emerged. The feedings were conducted during nine days, 

 at first with 7 flies and later with 25 flies. Data on the subject 

 appear in the following table: 



