CIRCULAR-SEAMED FLIES 3031 



are no greater than in man; but a few days afterward the eyes and nose begin to 

 run, the coat stares, a swelling appears under the jaw, and sometimes at the navel; 

 and though the poor creature continues to graze, emaciation commences, accom- 

 panied with a peculiar flaccidity of the muscles. This proceeds unchecked until, 

 perhaps months afterward, purging comes on, and the victim dies in a state of 

 extreme exhaustion. The animals which are in good condition often perish soon 

 after the bite is inflicted with staggering and blindness, as if the brain were affected. 

 Sudden changes of temperature produced by falls of rain seem to hasten the pro- 

 gress of the complaint, but, in general, the wasting goes on for months. When the 

 carcass is opened, the cellular tissue beneath the skin is found injected with air, as 

 if a quantity of soap bubbles were scattered over it. The blood is small in quantity, 

 and scarcely stains the hands in dissection. The fat is of a greenish-yellow color, 

 and of an oily consistence. All the muscles are flabby, and the heart is often so soft 

 that the fingers may be made to meet through it. The lungs and liver partake of 

 the disease. The stomach and bowels are pale and empty, and the gall bladder is 

 distended with bile. These symptoms seem to indicate poison in the blood, the 

 germ of which enters when the proboscis is inserted. The mule, ass, and goat 

 enjoy the same immunity from the tsetse as man and the game. Many large tribes 

 on the Zambezi can keep no domestic animals except the goat, in consequence of the 

 scourge existing in their country. Our children were frequently bitten, yet suffered 

 no harm; and we saw around us numbers of zebras, buffaloes, pigs, palas, and other 

 antelopes feeding quietly in the very habitat of the fly. There is not so much dif- 

 ference in the natures of the horse and zebra, the buffalo and ox, the sheep and the 

 antelope, as to afford any satisfactory explanation of the phenomenon." With the 

 gradual spread of civilization, it might be supposed that the ravages of this pest 

 would become lessened; but this does not appear by any means to be the case. 

 Writing in 1881, Mr. Selous remarks that " nowhere does this virulent insect exist 

 in such numbers as to the westward of the Victoria Falls, along the southern bank 

 of the Zambezi and Chobe. It is usually found in great numbers near the rivers, 

 becoming scarcer and scarcer as one advances inland, till at a distance of a few miles 

 it disappears, except in some particular patches of forest. Along the water's 

 edge they are an incredible pest, attacking one in a perfect swarm from daylight till 

 sunset; and without a buffalo or giraffe tail to swish him off, life would be unen- 

 durable. . . . About one in every ten bites (that perhaps touches a nerve) 

 closely resembles the sting of a wasp or bee, as it will cause one, when seated to 

 spring up as if pricked with a needle. ... I think that this plague of the tsetse 

 flies along the Chobe and Zambezi is due to the enormous numbers of buffaloes that 

 frequent their banks, as they always seem very partial to these animals. The bite 

 of this remarkable insect, as is well known, though fatal to all kinds of domestic 

 animals, is innocuous to every species of game and to man. A general belief exists 

 that among domestic animals, the donkey, dog, and goat are exceptions to this rule; 

 but this is a mistake, for I have seen all three die from the effect of its bites." 

 The genus to which the common tsetse belongs is represented in South Africa by 

 several species, all of which seem to be similar in habits. It ranges from 

 Somaliland in the east and the Congo in the west, southward as far as the 



