ROLE OF STOMOXYS CALCITRANS. 501 



experiments have yet been carried out in India, on the lines of those of 

 Kleine and Bruce in Africa, to show that, in an odd fly or two, ti-ypanosomes 

 may survive as in a culture medium and that possibly a sexual cycle may 

 occur. 



Baldrey(43) believes with Schat that there is evidence of a cyclical 

 development in flies infected with surra. He attempts to show that the 

 development of Tr. evansi in the fly is probably completed through a 

 mammal. He finds the trypanosomes in the fly quickly dying, and sees 

 a spore stage which is incapable of reproducing the disease. This suggests 

 to him that direct transmission by the fly is not the usual method since it is 

 rare to find trypanosomes in the proboscis of the fly immediately after 

 feeding. The longest time Stomoxys is kept alive for his experiments is 

 ten days. All feeding experiments were negative. Injections of flies were 

 found positive within twenty-four hours after infection. 



Leese(2i) fed wild Stomoxys, caught on surra animals, on a white rat 

 after five to twenty-one days of capture from infected hosts. The result 

 was negative for evidence of a cycle of development. Three experiments 

 were conducted with S. calcitrans in interrupted feedings of one-half- to 

 three-minute intervals. Fifteen flies transferred from a white rat to a 

 healthy guinea pig gave a negative result. Ten flies fed from surra 

 animals in the field transferred to a white rat proved negative. Ten flies 

 from an infected white rat to a healthy white rat produced a positive result 

 when fed — 1 on the first day, 2 on the second day, and 7 on the third 

 day. The flies were applied from tubes inverted over the animals. 



Koch (44) in a measure anticipated Kleine and Bruce in their classical 

 studies on cyclical development in insects. Koch's investigations in sleeping 

 sickness with Glossina "led him to conclude that the flies did not transmit 

 the disease by carrying the blood directly from an animal to another as 

 is usually supposed, but that the trypanosomes pass through a develop- 

 mental stage in the fly." 



Kleine (45) with the use of laboratory-bred Glossina was able to show 

 convincingly a distinct cycle of development of Tr. gambiense in the flies. 



Bruce and others, (46) working with Tr. gambiense and G. palpalis, found 

 that from a lot of 60 flies 1 survived on the seventy-fifth day after 

 infection and after previously infecting a monkey reproduced the disease 

 by subcutaneous inoculation. A tiny drop of the emulsion was sufficient. 

 Salivary glands, besides other organs, were infective in this fly. 



Bagshawe,(4'?) criticizing Bal drey's paper, says: "Such transmission ex- 

 periments as these should be continued with a large number of flies and, if 

 possible, for longer periods. In the case of the rat-flea and the tsetse-fly, 

 only a small percentage get a permanent infection with trypanosomes; 

 hence the odds against experiments with single flies succeeding are con- 

 siderable. No reliable evidence of a cycle of a pathogenic trypanosome 

 in Tabanus or Stomoxys will be obtained from a study of the parasites 

 found therein after infected feeds till the flies have been bred." 



Speaking of the carriers of surra in this connection, the author last 

 quoted remarks: "As it has been pointed out before, the first essential is 

 to breed and keep in captivity the flies which are under suspicion, and until 

 this has been done we shall remain in uncertainty whether there is or is 

 not a special development of the surra organism in the invertebrate host. 

 Our knowledge of the life history of the African species of trypanosomes 

 makes it very probable that there is." 



