362 Mammalian Trypanosomes of A frica 
Mosquitoes, etc. Whether or not mosquitoes played a part in the spread of 
human trypanosomes in Uganda we do not know. The French observers 
attach considerable importance to their intervention in the transmission of 
sleeping sickness in the Congo. 
On many of the islands culicine mosquitoes are very common. Bagshawe 
has shown, however, that the probabilities are against this factor having been 
of importance in Uganda; and the absence of any instance of direct trans¬ 
mission by insects other than Glossinae in the community of infected and 
healthy monkeys at the Entebbe laboratory—which presents a very fair 
experimental parallel to the conditions in an infected village, as far as mosquito 
and Stomoxys carriers are concerned—is of interest in this respect. 
PART IT. INFECTIVITY OF WILD LAKE-SHORE FLIES, 1920-21. 
The early Sleeping Sickness Commissions of the Royal Society in Uganda 
established the fact that freshly caught wild lake-shore G. palpalis, fed upon 
clean monkeys, infected the monkeys with a trypanosome indistinguishable 
from the organism responsible for the human disease. Since that time various 
observers have shown that the flies have maintained their infectivity in spite 
of the wholesale removal of human beings from their reach. 
The following section deals with the infectivity of the wild G. palpalis on 
Victoria Nyanza, past and present, as manifested bv feeding experiments 
and, more accurately, by actual dissection. 
A brief reference is made to the infectivity of wild G. morsitans in Uganda 
and Nyasaland. 
In these experiments attention has been devoted more especially to the 
polymorphic trypanosome which utilises the gut and salivary glands of the 
fly. In the feeding experiments the incubation period in the monkey is 
reckoned as seven days, and any flies which may have been fed on the monkey 
during this period are ignored in making the count. It is assumed that only 
one infective fly occurs in each positive experiment. 
A resume of previous experiments on the lake-shore infectivity in Uganda 
is given for comparison. It must be remembered that in these earlier experi¬ 
ments there was no question as to the identity of the trypanosomes obtained 
with T. gambiense. 
(a) Feeding experiments with wild flies. 
(a) Entebbe shore. May-Julv, 1903. Natives present, infected 1 in 3 or 5. No antelope. 
(First R.S. Commission.) 
Total flies fed ... ... ... 989-1360* 
Number of infections ... ... 3 
Percentage of infective flies ... 0-30-0-22. 
* In these experiments the monkeys were only examined at intervals of seven days. As 
batches of flies were being fed daily it is, therefore, impossible to estimate accurately the number 
responsible for each infection. 
