ZOOLOGY 
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death is sometimes long deferred and may not occur till several weeks after the 
infection. The victim gradually falls off in condition, suffers from extreme 
depression and loss of appetite, and ultimately dies from apparent blood- 
poisoning. 
Donkeys are far less subject to the poisonous character of its bite than 
horses or mules ; indeed it is said that the domestic donkey of East Africa 
which is only one degree removed from the Abyssinian wild ass, is impervious 
to its attacks, and certainly none of those animals have died from tsetse bite in 
British Central Africa. Major Lugard, I believe, has found on his expedition 
to Lake Ngami, that his donkeys were the only animals which survived the 
attacks of the tsetse. Dogs are killed by it and even cats will not resist its 
attacks when too frequent. On the Mwanza river, an affluent of the Shire nearly 
opposite to Katunga, the tsetse are so numerous that the only domestic animals 
which can be kept by the natives are fowls. Its bite on man produces absolutely 
no effect beyond the pain of the sharp puncture. It is hardly necessary to 
point out that the wild game of Africa—the buffalo, the antelope and the zebra 
—are quite unaffected by the tsetse bite, 1 though their nearest congeners among 
domestic animals—the ox, goat and horse—are killed by this fly. So far as we 
can judge from specimens classified in the British Museum the range of the true 
tsetse (Glossina morsitans ) extends from South Africa up to the Congo Basin, 
Lakes Mweru, Tanganyika and the borders of Somaliland. A closely allied 
species comes from the Congo Basin, the Niger Delta, and other parts of West 
Africa, a fly which, so far as we know, is equally poisonous. I am not sure that 
the actual tsetse is not found in the Niger Delta and in parts of the Congo 
Basin. Other species of Glossina inhabit other parts of Africa but do not 
appear to be poisonous. In the greater part of the Nigerian, the Central and 
the Egyptian Sudan the tsetse is absent, thus permitting a far more rapid and 
healthy development and conquest of these countries, as horses are abundant 
and can be employed to mount cavalry and transport travellers while for trade 
purposes mules and oxen can be employed ; and an unlimited number of cattle 
might be reared. 
The nature of the tsetse poison is not yet determined. It is not known that 
it injects any venom, it simply appears to insert the prong of the proboscis and 
suck the blood. Some have advanced the theory that there is no inherent 
poison in the tsetse itself, but that it inserts the germs of malaria. The 
argument sustained is that the wild animals of Africa have in the course of 
ages of adaptation become inured to malarial poisoning, but that they harbour 
in their blood the micro-organisms of malaria. These, passed on by the tsetse- 
fly, passing with infected proboscis from wild to tame animal, increase and 
multiply in the latter, which is not inoculated, and the beast dies not from a 
specific “ tsetse ” poison, but from malaria introduced into the blood by the 
tsetse. I confess, however, this theory, though ingenious, does not strike me as 
adequately accounting for all the facts. I cannot help thinking myself that 
the tsetse must secrete and introduce into the animal’s system a peculiar 
venom which in the human being causes the bite to itch; but if so the poison 
would be of a similar nature to that of the flea, the gnat and the midge, all of 
which produce different effects on different people. In my own case the bites 
of fleas and still more of bed-bugs (especially in tropical countries) produce 
positively feverish symptoms whereas many other of my fellow-countrymen 
make little or nothing of these attacks. 
1 For simplicity of diction I speak of the tsetse “bite.” It is of course a puncture of the proboscis. 
