356 Mammalian Trypanosomes of Africa 
infectivity of wild lake-shore Glossina palpalis and antelope; (2) an investi¬ 
gation of the transmissibility of trypanosomes by laboratory-bred G. palpalis, 
by both direct and cyclical methods; and (3) a study of the effects of different 
diets on the development of trypanosomes in these laboratory-bred flies. The 
observations and experiments appear to confirm the conclusions that the 
polymorphic mammalian trypanosomes of Africa are derivatives of a single 
species spread over the continent, and that they owe their present differences, 
great and small, largely to the influence of the mammal upon which, in the 
course of time, natural conditions have made them dependent as their main 
blood-host. Further discussion of the general problem will be attempted 
in the concluding section. 
In addition to actual experiments, certain extracts from the literature 
relevant to the points at issue, and such reflections and conclusions as have 
arisen from the consideration of the available facts, will be submitted from 
time to time. 
It is to be hoped that the interpretations here advanced will be received 
in the sense in which they are offered—not as dogmatic conclusions, but as 
tentative explanations conducive to further research and experiment along 
practical lines. A theory insusceptible of proof does not serve any useful end 
in dealing with a problem of such practical importance as the true relationship 
of the trypanosomes to man. The views put forward below may not be new, 
but, at any rate, they have not yet been presented with sufficient force to call 
forth decisive experiments. 
At the present time, under the control of Mr Fiske, an organisation is 
being established in Uganda to recover the long-suspended economic values 
of the fly-zone by a careful scheme of repopulation. This scheme is based on 
the assumption that, provided the contact between fly and man be not 
intimate, there is no danger of a recurrence of human trypanosomiasis in 
epidemic form. 
The fly and antelope on the Islands, where this scheme is being introduced, 
are still carrying trypanosomes apparently specifically identical with those 
described by workers in Uganda since 1909, and presumed to be T. gambiense. 
A certain number of natives, canoemen and fishermen, licensed and un¬ 
licensed, have, during the last 12 years, been extensively exposed to fly bite 
in the prohibited area. With the possible exception of two cases, no evidence 
of trypanosomiasis has been detected in any of them, and it is not absolutely 
certain that the two cases referred to had not visited the Mpologoma region, 
where an independent endemic form of the disease has existed for many years, 
separated from the Victoria Nyanza flv areas by a considerable extent of 
palpalis free country. As will be seen below, there is recent evidence that 
the trypanosome strains of to-day, in some places at least, are showing 
characters not before recognised in this fly zone. From the standpoint of the 
laboratory worker the point of practical importance is to determine as far 
as possible the effect, if any, of a prolonged sojourn in ruminants on these 
