6 7 
In April, just at the end of the dry season, a camp was made on the banks of the 
Upper Gambia river. Glossina palfalis was very numerous, but, strange to say, 
caused but little trouble ; there was a great deal of game in the neighbourhood. 
It has been reported that certain localities were infested with tsetses which at an 
earlier period were free from them. These statements have not been substantiated, 
and they seem sometimes to have resulted from insufficient observation. The possi¬ 
bility of their accuracy must not, however, be forgotten, especially since it is 
frequently asserted that the area over which Glossina exists is widening. 
Observations on captive Glossina pa l pal is.- During our attempts, 
in the Gambia," to transmit trypanosomes by the bites of tsetse flies, 
we found that they would not feed well in small cages and died in 
the course of two to four weeks. It was thought that this might have 
been one of the reasons why our Gambian experiments had been 
unsuccessful, and when we recommenced our experiments in the 
Congo we determined to reproduce, as nearly as possible, the natural 
surroundings of the fly by keeping them out of doors in larger cages 
containing water and growing grass. Cubical cages of wire gauze 
measuring 18 inches along each side were employed. In each cage 
was placed from 20 to 70 flies. These larger cages were kept in a 
large mosquito house, measuring 13 by 8 by 9 feet, made of wire 
gauze. It was placed in a thick clump of bamboos, distant about 
100 yards from the river. The flies were sheltered by the bamboos 
from the mid-day sun and, on two sides, from strong winds. Food 
was supplied to them by experimental animals, guinea-pigs and rat-, 
which were immobilised and placed in the cages. Glossina palpalis 
certainly lived better under these conditions than they had done in 
smaller cages in the Gambia. They frequently lived for over 30 days ; 
43 and 59 days were the longest lives noticed. In addition they 
seemed not to require food so often as had been necessary in the 
Gambia, and they were frequently left for 48 hours without an 
opportunity of feeding. This may be explained in part by their being 
out of doors and more exposed to cold and damp. Under such 
circumstances tsetses are certainly more sluggish in their movements. 
The disadvantages of this method of keeping flies were however 
great. It was almost impossible in such large cages to count exactly 
the number of flies which had fed or to estimate the number present 
They seemed to seek concealment and hid themselves in the smallest 
crevices. It was difficult to feed flies kept in this way on monkeys 
and the cages were too large to be easily transported. 
* Memoir XI, Liverpool School of Tropical Medicine. 
