'RYPANOSOMES IN TSETSE-FLIES AND OTHER DIPTERA. 215 
has T. gambiense given only negative results as regards a 
developmental cycle? If T. brucii is capable of developing, 
T. gambiense should be capable of doing so also. I can 
only explain my repeated failures to obtain development by 
the hypothesis that G. palpalis is not capable (in Uganda, 
at least) of acting as the true host of T. gambiense, but 
only of transmitting it by the direct method. Sleeping 
sickness, as is well known, has only been introduced into 
Uganda in comparatively recent times, having apparently 
come from regions further west. he appalling results 
produced by the epidemic brought about the appointment 
of our Commission, which carried on its investigations in 
Entebbe—that is to say, in a region where great mortality 
was taking place and the danger was most urgent. But 
in and around Entebbe G. palpalis is the sole species of 
tsetse-fly occurring, and has, therefore, obtained the sole 
credit of transmitting the disease which corresponds with it 
exactly in distribution. It is very possible that if our 
Commission had carried on its investigations in a region were 
more than one species of tsetse occurs, it would have been 
found that other species were equally effective. Brumpt, 
in 1904 (8), gave reasons for believing G. fusca to be 
also active in transmitting sleeping sickness.’ But more 
decisive on the point is the observation of Koch (21), 
who fed forty-two Glossine fusce and eleven G, tachi- 
noides, all of them young forms bred in captivity, on rats 
infected with T. gambiense, with the result that ten to 
twelve days later eight fusce and three tachinoides were 
found to be infected with trypanosomes that must be identified 
with T. gambiense, in view of the fact that virgin flies, as 
we may conveniently call them, were used for the experiment. 
No such result was ever obtained by me with G. palpalis; 
and I think it is a sound deduction from the observation of 
Koch, collated with my own experience, that G. palpalis is 
1 Ross (88), however, obtained “ entirely negative” results with G. fusca, 
but acknowledges that there was “not sufficient material in these experiments 
to come to any definite conclusion.” 
