causing Disease in Man in Nyasaland. 



521 



noted as occurring in the proboscis.* In this species they are noted on 

 several occasions as occurring in this position, but only in the^ wild-fly 

 experiments, not in the laboratory bred. It seems natural to expect that if 

 the salivary glands are swarming with trypanosomes that some of them will 

 sometimes appear in the hypopharynx and, moreover, in the wild flies some of 

 the infections of the proboscis are no doubt due to T. pecorum, T. simice or 

 T. caprce, all of which develop in the proboscis. 



Table V. — Laboratory- bred Flies. Result of the Dissection of the Infected 

 Flies found in the Positive Experiments. 



Expt. 



Time, 

 days. 



Proboscis. 



Proventri- 

 eulus. 



Fore-gut. 



Mid-gut. 



Hind-gut. 



Salivary 

 glands. 



1003 



33 









+ 







1003 



39 









+ 





? 



1723 



30 





+ + 



4 + 



+ + 



+ + 





1723 



30 





+ + 



+ + 



+ + 



+ + 





1723 



48 















2405 



32 









+ 







2405 



33 





+ + 



+ + 



+ + 



+ + 



+ + 



2405 



33 







+ 



+ 



+ 





2405 



33 







+ 



+ 



+ 





In Experiment 1003, two infected flies were found. The first had only a 

 gut infection and, unfortunately, it was found impossible to dissect out the 

 salivary glands of the second. Neither had an infection of the proboscis. 



In Experiment 1 723, three infected flies were found. The first and second had 

 the alimentary tract swarming with flagellates, but none in the salivary glands. 

 The third was found on dissection to be free from trypanosomes throughout. 

 This is curious because this fly had been isolated in a glass tube as an 

 infective fly, and had, when used alone on a rat and rabbit, infected both 

 these animals. The fly remained alive in the tube for 13 days, and the only 

 explanation that can be given is that in this case the trypanosomes disappeared 

 absolutely from the fly some few days before its death. This was the first 

 time this had been observed to take place, and it was thought to be a 

 remarkable phenomenon and difficult to credit, until another example of the 

 same kind was observed. It must, therefore, be held as probable that an 

 infective fly, with presumably both salivary glands and alimentary tract 

 swarming with trypanosomes, can lose all these flagellates and become non- 

 infective. 



In Experiment 2-405, four infected flies were found. Three of these were 

 infections limited to the gut. The fourth was a good example of a salivary- 



* Ibid., B, vol. 82 (1910). 



