496 



MITZMAIN. 



through feeding can infection be transported by the fly. This 

 would involve the introduction from without of infective ma- 

 terials into the punctured skin of the host. Such external factors 

 might include excretory contamination, contamination from the 

 insect's pulvillus, and more remotely that from hairs of the in- 

 sect's body or that from the wings. 



A series of experiments was performed to decide whether or 

 not the wound caused by the fly's proboscis was suitable for 

 the entrance of infective material. In these trials a varying 

 number of bred Stomoxys flies were induced to bite healthy 

 guinea pigs whose skin was thoroughly shaved but not abraded. 

 A generous platinum loopful of blood freshly drawn from the 

 ear of a surra guinea pig was rubbed into the fresh bite imme- 

 diately after each fly was withdrawn. In this series of ex- 

 periments the infected blood used was taken from guinea 

 pig T, which reacted to inoculation of a single proboscis of a 

 fly fed on a surra animal. Guinea pig T, which is accounted for 

 in Table XV, was used here when its blood swarmed with surra 

 trypanosomes. In every instance, after a lot of flies were 

 fed, the area of the skin covered by the inverted test tube was 

 vaccinated with a saline solution containing heavily infected 

 surra blood. The following table contains information as to 

 the work done on this subject: 



Table XIV. — Results of rubbing infected blood into wounds caused by 

 proboscides of flies. 



Number of 

 bites. 



Guinea pig 

 used. 



Results. 



8 

 20 



7 

 13 



121 

 105 

 102 

 103 



Negative. 

 Do. 

 Do. 

 Do.« 



» Reacted six weeks later to inoculation of surra blood. 



To what extent the faeces from infected flies are contaminated 

 has not been systematically determined. One experiment to de- 

 termine the range of this infection was tried up to eighteen 

 hours with faeces of infected flies. According to the results, 

 although degenerative forms were detected microscopically, the 

 injected material was devoid of infective trypanosomes. The 

 experiments were concluded in each case with a negative result. 

 For the present, therefore, with the evidence at hand, the pos- 

 sibility of infection by fly dejecta rubbed into the bitten skin 

 is considered as nil. 



