252 Prof. Minchin, Lieut. Gray, and late Lieut. Tulloch. .[July 10, 



G. palpalis we were never able to obtain any definite proof that it fed on 

 anything but blood. It is therefore difficult* to understand how a parasite of 

 the tsetse-fly itself could be conveyed from one fly to another except by the 

 hereditary method. We have a single instance to record which certainly 

 suggests hereditary transmission of these trypanosomes. A tsetse-fly was 

 bred in the laboratory in August and was fed for two months on fowls, which 

 were unfortunately also used for feeding our stock of tsetse-flies in our 

 breeding cages. On October 9, the fly was fed on a monkey showing very 

 scanty trypanosomes (T. gambiense) in its blood. The next day, 21 hours 

 later, this fly was dissected and found to contain a few scanty T. gambiense, 

 one of which is figured on Plate 12, fig. 14, and vast swarms of 

 T. grayi (Plate 13, figs. 23 and 28). It is obvious, therefore, that this fly was 

 either infected with T. grayi when it emerged from its pupa or that it 

 became infected from one of the fowls which had possibly been infected in 

 its turn by the fresh flies which fed on it. It may be mentioned in this 

 connection that experiments directed towards obtaining flies infected with 

 T. gambiense by the hereditary method, that is to say, by breeding from flies 

 fed continually on infected animals, gave no result. 



In conclusion, one remarkable experiment of ours may be mentioned. At 

 our camp on Nsadzi, referred to above, we fed a large number of freshly 

 caught Kimmi flies on a goat which we obtained from natives on the island. 

 We then dissected these flies and, to our astonishment, could not find 

 trypanosomes in a single one of some 500 flies which had so fed, whereas in 

 other Kimmi flies, caught at the same time, which had fed on our other 

 experimental animals (monkeys, etc.), trypanosomes were present in the 

 usual proportion. We then prepared some goat's serum and added a drop of 

 it to the contents of a fly's intestine teased out on a slide, which contained 

 T. grayi in large numbers. Another drop of this same goat's serum was 

 added to a preparation of T. gambiense obtained from an infected rat and the 

 two preparations watched. It was found that in the preparation of 

 T. grayi the trypanosomes rapidly became immobile and died off, while the 

 T. gambiense remained active. We then tried the same two experiments 

 over again, using human serum instead of the goat's serum, and then found 

 that the trypanosomes were not affected in either case. This result seems 

 to us to furnish an additional means of distinguishing between T. gambiense 

 and T. grayi. 



