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On the Occurrence of Encystation in Trypanosoma grayi Novy, 

 with Remarks on the Method of Infection in Trypanosomes 

 generally. 



By E. A. Minchin, M.A. 



(Communicated by Professor E. Bay Lankester, F.K.S. Eeceived November 3, — 



Eead November 8, 1906.) 



In a tsetse-fly dissected and examined by me in the laboratory of the 

 Sleeping Sickness Commission at Entebbe, Uganda, it was found that not 

 only was the intestine swarming with Trypanosoma grayi, but the proctodeum 

 also contained vast numbers of trypanosomes. Under moderate magnification 

 they could be seen in dense clumps attached to the wall of the proctodeum, 

 each clump having a superficial resemblance to a patch of mould, the whole 

 mass, however, vibrating with the movements of the flagella. It was rather 

 uncommon to find these parasites in the hind gut, and I at once made smears 

 from different regions of the digestive tract, and carefully preserved and 

 stained them. As it was but a short time before my departure from Entebbe, 

 I was not able there to do more than glance at my preparations, but I noticed 

 at once an important fact, which since my return to England I have been 

 able to confirm and extend by careful study of my slides : namely, that in 

 the hind gut the trypanosomes are in process of becoming encysted. Before 

 proceeding to describe the encystment, I will say a few words about the 

 conditions of the occurrence of these trypanosomes, and the manner in which 

 they were preserved. 



The tsetse-fly in question was one of a batch caught by our fly-boys 

 at Entebbe on November 2, and fed the next day on a monkey infected with 

 Trypanosoma gambiense from the cerebro-spinal fluid of a Sleeping Sickness 

 patient. On every subsequent day these flies were fed on a healthy guinea- 

 pig, and a certain number of flies were dissected daily and examined, until the 

 batch was used up. Without going into details, it is sufficient to say that 

 T. gambiense was found sparingly in the flies dissected up to 96 hours, that is 

 to say, on November 4, 6, and 7. After this date T. gambiense disappeared 

 completely and could not be found in any of the flies dissected. The fly in 

 which the encystment was discovered was dissected on November 14. It 

 must, of course, have been infected with T. grayi when caught, and, as I 

 have stated, it had been kept 11 days in the laboratory and fed daily. At 

 the autopsy it was found to be gorged with blood, and with all its organs 

 perfectly normal and healthy in appearance. I examined the salivary 

 glands and genital organs (testes and vesiculae seminales) without finding 



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