BIG GAME AND TSETSE FLIES 
119 
it is frequently found to be confined to comparatively narrow 
strips of country of considerable length known as fly belts. 
Sometimes these belts are very sharply defined, so that within 
a few hundred yards of apparently uniform country the 
traveller can pass from an area swarming with flies to one in 
which the fly is entirely absent. 
The cause of this singular distribution is altogether obscure. 
It is certainly not dependent on the presence or absence of 
game ; a narrow fly belt may extend through a wide area with 
abundance of game or through a region where game is ex- 
ceedingly scarce or altogether absent. There are certain 
observations of H.B.M. Consul of Louren^o Marques, Mr. 
R. C. F. Maughan, which show that the tsetse fly sometimes 
sucks vegetable juices, and it is conceivable that the occur- 
rence of fly belts is partly dependent on the presence of certain 
plants, which we could readily understand might be confined 
to belts dependent on the geological out-crops. There is, 
however, at present no scientific evidence to warrant such a 
view. 
Trypanosomes of many kinds have been found in a great 
variety of fishes, amphibia, reptiles, birds, and mammals. In 
the majority of cases it appears that these parasites have no 
obviously prejudicial effect on the host. The particular 
trypanosome (T. brucei) which causes the nagana disease in 
domestic animals has been found in the blood of jackals and 
antelopes, and there is little doubt that it occurs in many 
different kinds of animals. The tsetse fly while sucking blood 
conveys the parasite from the first host, where it is innocuous, 
to the second host, where it causes a malignant disease. 
The question whether the local destruction of game animals 
would have any permanent effect in lessening the fly scourge 
and reducing the occurrence of nagana has received very 
careful consideration, and it may be said by the evidence given 
hereafter that it is exceedingly doubtful whether any per- 
manent beneficial effect would be obtained by such action. 
Some of the reasons may be summarised as follows : 
1. The distribution of the tsetse fly in belts is not dependent 
on the abundance or scarcity of wild animals. 
2. Trypanosomes are abundant in many kinds of animals, 
