H. L. Duke 
373 
Whether or not the animal was seriously inconvenienced by the trypano¬ 
some it is impossible to say: certainly he gave the impression of feeling the 
malarial attack more than the subsequent trypanosome infection. 
The strain employed in this experiment was the wild-fly organism from 
Monkey 88, which represented the second passage by direct transmission. 
There are at present two other chimpanzees at the laboratory, the younger 
of which a month or so after its arrival developed an attack of malaria in 
which the parasites appeared to be identical with those seen in the original 
chimpanzee. The attack thoroughly upset the little animal for three or four 
days, after which he renewed his interest in life. The other animal is an old 
male, grey-haired all over his body and with what appears to be commencing 
arcus senilis. He allows no liberties to be taken with him at present, and no 
examinations have as yet been made of his blood. 
(h) Conclusions. 
The animal-reaction experiments of this section show: 
(n) That the situtunga antelope on Damba Island at the end of 1920 
harboured a polymorphic trypanosome whose characteristics are different in 
several respects from those of the polymorphic organism isolated from the 
same antelope species on Damba in 1912 (Duke, 1912 6). Whereas the 1912 
strain agreed with T. gambiense, the 1920 strain shows many of the characters 
usually assigned to T. brucei. 
(6) That the disease in monkeys and in sheep caused by the Damba 
antelope strain of 1920 is on the whole more virulent than that produced 
in these animals by the wild-fly strain from the mainland; the trypanosome 
strain derived from wild Damba G. palpalis occupies an intermediate position 
as regards its pathogenicity towards monkeys. 
(c) That the general virulence towards laboratory animals of the Damba 
antelope strain of 1920 is, on the average, greater than that shown by the 
other two strains investigated. 
(d) That posterior-nuclear forms have been developed by all the three 
strains, but appear to be more frequent with the Damba antelope strain. 
(e) That the virulence of the human strain, recently isolated from a native 
who was probably infected in the Mpologoma endemic area, is very much 
less towards monkeys, guinea-pigs and rabbits. It was found difficult to 
bring about the infection of monkeys with human blood containing living 
trypanosomes, and subsequent passage in these animals was always charac¬ 
terised by a long incubation period and, during the first six months at any 
rate, rarity of the parasites in the peripheral blood. Several attempts to infect 
guinea-pigs and rats from first and second-passage monkeys failed. No 
posterior-nuclear forms were ever seen in blood slides from the animals infected 
with the human strain. 
(/) That the baboon is immune to the human, the antelope, and the 
wild-fly strains of trypanosomes, whether infection be attempted by the 
