894 
INSECTS AND THEIR RELATION 
and mules. There is one, however, which we obtained from 
Yoi, which did not affect any inoculated animal except mules 
and donkeys. Oxen, sheep, dogs, rats, guinea-pigs, and rabbits 
were not susceptible ; yet the trypanosome was so virulent as 
to kill mules and donkeys within six days of inoculation, 
and to reproduce most exaggerated symptoms like those of 
horse-sickness. 
Opposed to this group, the majority of trypanosomes will 
affect both domestic and laboratory animals — usually, how- 
ever, with variations in course, or symptoms which can be 
employed as bases for classification. Thus, one of the most 
common and serious infections of horses in German East 
Africa does not kill cattle, although these animals may harbour 
the trypanosome for years and therefore act as reservoirs. 
Another form, which killed many cattle in the Fort Hall 
epidemic of two years ago, is much less pathogenic to horses ; 
for although one or two died of an acute disease, the majority 
recovered spontaneously, and are still alive and well over two 
years after infection. 
It will be clear to you now that tsetse-fly disease is not 
due to the fly, but to the particular species of trypanosome 
conveyed ; and with this knowledge it will be understandable 
how diverse the experience of different men will be. The one 
may lose all cattle ; another all horses. A third will assure 
you that he has an absolute cure or preventive, because he 
did not lose his horse or his ox when a fourth owner did. These 
results are due to nature : due to the species of trypanosome 
involved, and rarely to any intervention ; for we must still 
regret with the Lieut. -Governor of the Punjab in 1880, that 
a cure has not yet been found. 
The time at my disposal is too short to enter into the vexed 
question of game and its relation to the Glossinae, and I give 
the Hon. Secretary the free tip that Mr. Percival be asked 
to afford the Society the benefit of his large experience on 
this point. But I have said enough to prove to you that the 
tsetse must acquire the trypanosome infection before it becomes 
harmful ; and we know that many varieties of game can harbour 
trypanosomes in their blood and serve as reservoirs for these 
diseases. 
