OPERATION OF TSETSE POISON. 95 



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 wild 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 na- 

 tives 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 

 color as the mandibles come into brisk operation. The previ- 

 ously shrunken belly swells out, and, if left undisturbed, the fly 

 quietly departs when it is full. A slight itching irritation fol- 

 lows, but not more than in the bite of a musquito. 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 few days after- 

 ward the following symptoms supervene : the eye and nose begin 

 to run, the coat stares as if the animal were cold, a swelling ap- 

 pears 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 afterward, purging comes 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- 



