Diseases of Domestic Animals in Nyasaland. 



63 



in all the infected flies found in Experiment 1847 this was done, with the 

 result that the hypopharynx was found invaded by trypanosomes in four out 

 of the seven. 



Plate 6 represents, at a magnification of 500 diameters, the labial cavity 

 and hypopharynx of an infected fly. While the labial cavity contains 

 clusters of large ribbon-like trypanosomes, the hypopharynx is swarming 

 with small active forms resembling the original blood forms, from which 

 the developmental cycle arose. "When the plate is examined the facility 

 with which a tsetse fly can infect an animal will no longer be a matter of 

 wonder. 



Finally, from the table it will be seen that in no case were the salivary 

 glands invaded. 



The Methods used ix the Examination of the Elies. 



The flies were dissected as described in a previous paper.* An additional 



method of examining the contents of the hypopharynx was to isolate 



infective flies by putting each fly into a separate tube, numbering it, and 



feeding the fly on a susceptible animal with a corresponding number on its 



cage. The numbers on the cages of animals which became infected indicated 



the tubes containing infective flies. These, when thus identified, were 



starved for 24 hours, in order to make them hungry. A tube Contamina- 

 te 



one of the infective flies was then taken, and its mouth being covered with 

 mosquito netting was applied to a large cover-glass placed on a man's finger. 

 The hungry fly at once attempted to feed through the glass, and in poking 

 about with its proboscis smeared the surface of the cover-glass with saliva. 

 This was immediately fixed, stained with Gienisa, and examined. 



The Trypanosomes fouxd ix the Proboscis. 

 Eeference to the table above will show that in Experiment 754 two infected 

 flies were found, one on the 37th day after feeding on an infected monkey, 

 and one on the 5 0th day, and that the labial cavities of both flies were 

 infected. 



The fly that died on the 50th day was the one which no doubt actually 

 infected the healthy monkey, since the animal showed trypanosomes seven 

 days after the death of this fly and no other infected fly was found. As these 

 two flies died before they were isolated, the method of inducing them to 

 salivate on a cover-glass was not used. When, however, the two proboscides 

 were examined in a drop of normal saline solution under a cover-glass, 



* ' Roy. Soc. Proc., ! 1911, B, vol. 83, p. 513. 



