16 THE PRESIDENTIAL ADDRESS. 
was no suspicion at the time that it had any connection with the 
tsetse-fly. 
At this time a very enlightened administrator, the late Sir Walter 
Hely-Hutchinson, was Governor of Natal and Zululand, and it was due to 
him that the investigation of the cause of the Zululand outbreak was at 
once undertaken. ‘ 
As I happened to be stationed in Natal at this time, I was chosen to 
undertake the work, and at once started on the long journey, mostly by 
ox-wagon, to the scene of the outbreak. 
On examination of the blood of the nagana cattle, a minute active 
flagellated protozoal parasite, belonging to the genus Trypanosoma, was 
discovered, and after many experiments on dogs, horses, and cattle it was 
decided that in all probability it was the cause of the disease. 
Trypanosomes had previously been described in the blood of rats and 
horses in India by Timothy Lewis and Griffith Evans, but nothing was 
known as to the mode of their transmission from animal to animal. 
It seemed as if the discovery of the nagana trypanosome would have 
ended the investigation in Zululand without any means of preventing the 
disease being discovered, but another observation made at this time threw 
more light on the subject. 
In the low country between the high ground, on which the nagana camp 
was situated, and the sea there happened to be a so-called ‘ Fly belt.’ 
Every schoolboy had read about the tsetse-fly in books of travellers 
and hunters, especially in those by the most famous of them all, David 
Livingstone the missionary, and out of curiosity I decided to find out what 
happened when an animal was bitten by the fly, or, as it was termed, fly- 
struck. 
Natives were therefore sent with cattle and dogs into this ‘ fly country,’ 
with orders to form a camp and expose the animals to the bites of the fly. 
This was done and it was with great surprise that on their return to the hill 
the blood of these fly-struck animals was found to contain the same parasite 
as that found in the nagana cattle. 
Nagana and tsetse-fly disease were finally proved to be identical. The 
tsetse-fly disease was shown to be caused, not, as had been believed, by the 
poisonous bite of the fly, but by the transference of a protozoal parasite 
from the fly to the animal in the act of sucking blood. 
Now the question arose as to where the fly found the parasite. As 
the tsetse-flies constantly lived among and fed on wild game, such as buffalo 
and antelope, these animals were suspected. Their blood was examined, 
