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exodus—the antelope, and the hippopotamus would be increasingly drawn 
upon by the fly for mammalian blood. 
(9) We know that T. gamhiense will survive for many months in the 
blood of the situtunga, and the antelopes must have become infected with 
the human trypanosome as the departure of man brought them into ever- 
increasing contact with the tsetse. From 1909 onwards, Tragelaphus spekei 
and the hippopotamus have constituted the mammalian food supply of the 
fly, and ipso facto, the reservoir of its trypanosomes. 
(10) At the present day antelope swarm on some of the larger and a few 
of the smaller islands, and have extended their range since 1912 to islands 
on which, at that time and previously, they were unknown. Their numbers 
are enormous and their relation to the fly is very intimate. In 1912 the wild 
fly and the situtunga were still carrying a polymorphic trypanosome whose 
general behaviour was that of T. gambiense, and there appears to be no reason 
to doubt that the polymorphic trypanosomes in the situtunga and wild G. palpalis 
in the prohibited area of Lake Victoria at the present day are the descendants of 
the T. gambiense which occurred in man at the time of the epidemic. 
(11) At the present day certain of these wild strains differ to a greater 
or less extent from the 1912 types; but as far as is known, there has been, 
since 1909, no introduction of fresh strains from outside, so that this cannot 
be the explanation of these differences. In the last few months evidence has 
been acquired of the occurrence of significant variations in the virulence and 
morphology of the trypanosomes on Damba, the island where the relations 
between fly and buck are more intimate, probably, than anywhere else. The 
variations observed tend towards the assumption of the characters typical 
of T. brucei. 
(12) T. brucei, when it occurs in a fly-infested game region, is, as a rule, 
readily recoverable from both game and fly. Had such a trypanosome existed 
in the lake-shore palpalis area so thoroughly investigated by various observers 
in Uganda, it seems incredible that its presence should not have been detected 
by 1912. As stated above, trypanosomes of this type have not, as far as I 
can ascertain, been recorded from any purely palpalis area outside Uganda 
Protectorate. 
(13) The difference between the only two strains so far recovered from 
Sesse situtunga is clearly marked. On the other hand, it must be admitted 
that, until the recovery of this second buck strain, no particular care was 
taken to search for posterior-nuclear forms in the strains obtained from lake- 
shore flies. These strains all produced more or less chronic infections in 
monkeys, but relatively few sub-inoculations were made into small animals. 
As regards the 1912 antelope strain, however, it is quite certain that posterior- 
nuclear forms did not occur, as this trypanosome was carefully examined at 
the time to see whether it showed any points of resemblance to the brucei 
type (Duke, 1912 b). 
(14) While it is thus qiossible that posterior-nuclear forms occurred in 
