388 
Mammalian Trypanosomes of Africa 
than with T. brucei, as regards virulence in laboratory animals and the absence 
of posterior-nuclear forms. 
(3) With one certain and one doubtful exception, wherever the brucei 
type of trypanosome has been recovered from game or stock in a palpalis 
area, there have always been other tsetse species present in that area, and 
investigation has often actually proved that it is the other species that 
transmit this trypanosome in nature. From the foregoing considerations— 
which must be taken in conjunction with what has previously been said re¬ 
garding “species'’ (see Introduction)—it seems reasonable to conclude that 
the relatively avirulent polymorphic trypanosomes of palpalis areas , be they found 
in man, stock, or game, belong to a single natural species. This species is capable, 
on occasion, of parasitising man, and when it does so, the trypanosomes found in 
his blood are those which have for years been called T. gambiense. 
(4) Now the only two instances, where a trypanosome possessing the 
characters of the brucei group has been recovered from a pure palpalis region, 
occur in areas which have for years been uninhabited by man and where 
antelope abound, namely the Sesse Islands and Kiraro Lake near Lake George. 
There is, apparently, no region in Africa where antelope play such an important 
part in the dietary of G. palpalis as on the Sesse Islands at the present day, 
and where, in consequence, the polymorphic trypanosomes carried by this fly 
have an antelope as their almost exclusive host (the hippopotamus has been 
shown by Carpenter to be much less patronised by this fly than the situtunga, 
where both are available as food animals). 
(5) In the old days the situtunga must have obtained their mammalian 
trypanosomes from G. palpalis ; leeches and ticks do not appear to have played 
any part in the transmission of these parasites. But let us consider the 
distribution of trypanosomes on these islands to-day. In neither the wild 
fly nor the antelope have trypanosomes of the nanum-pecorum group ever 
been detected, and these organisms showed great reluctance to undergo full 
cyclical development in laboratory-bred flies at Mpumu. On the other hand 
T. vivax and T. uniforme are common in both buck and fly. In addition, we 
find in both buck and fly the polymorphic organism described from Damba. 
(6) Whether the Sleeping Sickness epidemic was started by the entry of 
T. gambiense from some neighbouring endemic area or was due to an already 
existent organism whose spread was favoured by the terrible famine in 
Busoga, it is certain that a polymorphic trypanosome described as T. gam¬ 
biense was present in the blood of an enormous number of human beings from 
1901 to 1909 in the Uganda Lake palpalis areas. 
(7) The part played by direct transmission in the spread of this epidemic 
we shall never know. It is certain, however, that a relatively large percentage 
of the wild fly must have been cyclically infected with the human trypano¬ 
some. 
(8) With the gradual depopulation of the area by removals and by death, 
the cattle—the majority of which did not leave the islands until the final 
