Chap. IV. 
OPERATION.OF TSETSE POISON. 
81 
the ox, horse, and dog. In this journey, though we were not 
aware of any great number having at any time lighted on our 
cattle, we lost forty-three fine oxen by its bite. We watched the 
animals carefully, and believe that not a score of flies were ever 
upon them. 
A most remarkable feature in the bite of the tsetse is its 
perfect harmlessness in man and '\¥ild animals, and even calves 
so long as they continue to suck the cows. We never experienced 
the slightest injury from them ourselves, personally, although we 
lived two months in their habitat^ which was in this case as 
sharply defined as in many others, for the south bank of the 
Chobe was infested by them, and the northern bank, where our 
cattle were placed, only fifty yards distant, contained not a single 
specimen. This was the more remarkable, as we often saw 
natives carrying over raw meat to the opposite bank with many 
tsetse settled upon it. 
The poison does not seem to be injected by a sting, or by ova 
placed beneath the skin, for, when one is allowed to feed freely on 
the hand, it is seen to insert the middle prong of three portions, into 
which the proboscis divides, somewhat deeply into the true skin; 
it then draws it out a little way, and it assumes a crimson colour 
as the mandibles come into brisk operation. The previously 
slmmken belly swells out, and, if left undisturbed, the fly 
quietly departs when it is full. A slight itching irritation follows, 
but not more than in the bite of a mosquito. In the ox this 
same bite produces no more immediate effects than in man. It 
does not startle him as the gad-fly does; but a feiv days after¬ 
wards the following symptoms supervene: the eye and nose begin 
to run, the coat stares as if the animal were cold, a swelling 
appears under the jaw, and sometimes at the navel; and, though 
the animal continues to graze, emaciation commences, accom¬ 
panied with a peculiar flaccidity of the muscles, and this proceeds 
unchecked until, perhaps months afterwards, purging conies on, 
and the animal, no longer able to graze, perishes in a state of 
extreme exhaustion. Those which are in good condition often 
perish soon after the bite is inflicted with staggering and blind¬ 
ness, as if the brain were affected by it. Sudden changes of 
temperature produced by falls of rain seem to hasten the progress 
of the complaint; but in general the emaciation goes on unin- 
G 
