THE PRESIDENTIAL ADDRESS. 17 
and before long it became evident that the wild animals acted as the 
reservoir of the disease, the trypanosomes living in their blood as harmless 
parasites. When the tsetse-fly fed on blood containing the trypanosome 
it became infected, and was capable by its bite of giving rise to a fatal 
disease in cattle, horses, or dogs ; whereas if it fed on a wild animal nothing 
happened, as the wild game are immune to the disease, much in the same 
way as the goat is immune to Malta fever. 
Now that the natural history of the disease had been so far worked out 
it was evident that its prevention might be attempted. 
This can be done in any of three ways : by getting rid of the wild game, 
the reservoir ; or by getting rid of the fly, the vector or carrier ; or, lastly, 
by removing the cattle, horses, and dogs to a safe distance from the “ fly 
country.’ 
This work on nagana led later, in 1903, to the discovery of the cause and 
mode of prevention of sleeping sickness. 
Sleeping Sickness. 
About the beginning of the century an epidemic of this disease raged 
round the shores of Lake Victoria in Central Africa. It had been introduced 
into Uganda from the West Coast, where it had been known for many years 
| 
as a curious and unaccountable disease. It was observed that although 
the disease spread in a West African village from man to man apparently 
by contact, no such thing occurred among natives exiled from their homes. 
The disease never spread if introduced into native compounds in the 
West Indies or America, however closely the slaves might be herded 
together. 
_ The disease remained shrouded in mystery and nothing had been done 
in the way of prevention, until the matter was taken up by the Royal 
Society of London in 1902 and a Commission sent out to investigate. 
It is not necessary to go into details ; suffice it to say that after one or 
- two false starts the Commission in 1903 came to the conclusion that the 
disease was caused, as in nagana, by a species of trypanosome. 
The question of the distribution of sleeping sickness in Uganda was 
then taken up. This disclosed the remarkable fact that the disease was 
restricted to the numerous islands in the northern part of the lake and 
to a narrow belt of country skirting the shores of the lake. In no part of 
Uganda were cases found more than a few miles from the lake shore. 
The next important step in the working out of the etiology was made 
_ when it was shown that the distribution of the disease was identical with 
1924 C 
