274 OTHEE FLIES SEEM NOT TO CAEEY PAEASITE. 



shown by the fact that up here at Ubombo, where we have 

 several species of these pests, no single instance of the disease 

 arising spontaneously has occurred, although healthy horses, 

 cattle, and dogs have been constantly and closely associated with 

 those sufiering from the disease. Why this should be so is at 

 present a mystery, and it is to be hoped that some point may be 

 discovered which will throw light on the subject. There may be 

 some anatomical peculiarity in the Tsetse which enables it to act as 

 carrier, or there may be some vmdiscovered fact in the life-history 

 of the parasite associating it with this particular species of fly. 



" One fact, however, must be borne in mind, and that is the 

 enormously gi'eater number of Tsetse-flies in the Fly Country than 

 any other species of blood-sucking fly met with there, I have 

 seen as many as 200 Tsetse-flies on a horse at the same time ; 

 and when it is stated that I have often caught and put into a 

 cage singly some fifty Tsetses in half-an-hour, some conception may 

 be gained of the enormous number of Tsetse-Hies which may 

 visit a horse during its sojourn for one day in the ' Fly.' 



" The act of feeding is remarkably quick. From the moment 

 of settling on the animal until the fly is fully blown out with 

 blood is often as little as twenty to thirty seconds. But still this 

 does not explain why none of the healthy animals up here on the 

 top of the Ubombo have become infected by their diseased neigh- 

 bours, because we have many small stinging flies — some species 

 probably of Stomoxys — which cause drops of blood to exude from 

 the legs and ears of our animals. But this I can assert, and it is 

 an important point, that in no single case, as far as I am aware, 

 has any case of the disease occurred up here due to infection fi'om 

 the diseased to the healthy. 



" That the Tsetse-fly can act as a cannier of the parasite is, I 

 think, shown by the following experiments." 



Details, with charts, are given of two experiments in which 

 eight flies were allowed to feed on a healthy dog immediately 

 after having fed for a short time on a dog suffering from the 

 disease. The procedure was repeated on several days, and in 

 each case on the sixth day after the flies were last fed the dog 

 was found, by microscopical examination of his blood, to be 

 suffering from the disease. The author adds : " Up to the present 

 then from these two series of experiments it is seen in the firftt 

 place that the fly per se does not give rise to any local or general 

 disease, and this is further borne out by other experiments in 

 which I placed minced up flies under the skin of dogs without any 

 results, and secondly it proves that the fly can act readily as a 

 carrier of the Fly Disease from affected to healthy animals " (p. 6). 



" (c.) How long does the Tsetse-fly retain this infective 

 power ? 



" Now as one of the main objects of this investigation is to 



