SLEEPING   SICKNESS.                            21
It is quite possible that one of these animals was acting as a
reservoir to the other, but as neither seemed to suffer from the
effect of the trypanosome, the subject in this particular instance
is of academic interest rather than of practical importance.
The second method of injecting the blood of a newly killed
animal into a susceptible animal was also carried out in a number of
instances, but without success. In most cases it was the blood of
lake shore birds that was used, but that of hippopotamus, crocodile
and antelope was also injected. It was not surprising that this
method failed because where reservoirs exist they generally only form
a very small proportion of the class of animals they represent. Then
the blood has to be injected at once into the test animal, which in this
case meant that monkeys had to be carried about on all shooting
expeditions. This involved the fallacy that by taking a susceptible
animal into a fly belt known to be infective it is liable to contract
the disease naturally.
The animals to which most attention was paid were those found
most frequently on or near the lake shore. As a representative of
the birds the common fowl had to be used, as it was not found pos-
sible to experiment with the divers, cormorants and other species
actually found on the lake shore.
Next the domestic cattle were examined.
Lastly the wild antelope which infest the shores were subjected
to special attention.
A number of attempts to transmit Sleeping Sickness by means
of laboratory bred tsetse flies from infected or potentially infected
fowls to clean monkeys were made-but with negative results.
The conclusion was that the domestic fowl cannot act as a reser-
voir of the virus of Sleeping Sickness, but we pointed out that this
negative result does not necessarily apply to the birds found
naturally in the fly area.
Native cattle were then examined. The importance of the
animals being a reservoir is obvious, for they go down to the water's
edge daily to drink and generally live amongst the people in or about
the kraals. They might act readily as a go-between if proved to be
susceptible to infection with Trypanosoma Gambiense.
The experiments detailed in Paper No. 8 (vide Summary, page
37) prove that cattle are susceptible to Trypanosoma Gambiense,