540 REPORT—1905. 
organisms multiply in the blood by simple longitudinal division, and often 
become so numerous as to number several millions in every drop of blood. They 
are sucked, along with the blood, into the stomach of the fly, live and multiply in 
the alimentary tract for several days, and, when the fly has its next feed on an 
animal, take the opportunity of gaining access to the blood of the new host, and 
so set up the disease. 
Let me now throw on the screen a representation of the tsetse-fly (Glossina 
morsitans) which does all the mischief. Experiments were made which showed 
that the fly could convey the parasite from affected to healthy animals for at 
least forty-eight hours, It is a curious fact that among all the blood-sucking 
flies the tsetse-fly alone has this power, and up to the present the cause of this 
has not been thoroughly cleared up. Lately, however, evidence has been brought 
forward to show that an enormous multiplication ,and development of the 
trypanosomes take place in the tly’s intestine, a few trypanosomes multiplying 
to masses containing numberless parasites within twenty-four hours. Now, if 
this multiplication only takes place in the intestine of the tsetse-fly, and fot in 
the other kinds of biting flies, this would probably account for the curious con- 
nection between the tsetse-fly and the disease, This multiplication of the trypano- 
somes in the tsetse-fly was discovered by Gray and Tulloch,two young Army medical 
officers, while working in Uganda on ‘Sleeping Sickness’ during the present year. 
Not only was it found that the tsetse-flies could convey the disease from sick 
to healthy animals, but it was also proved that the wild tsetse-flies brought from 
the ‘Fly Country’ and straightway placed on healthy animals also gave rise to the 
disease. The question then arose as to where the tsetse-flies living in the ‘Fly 
Country’ came by the trypanosomes. There were no sick horses or cattle in the 
‘Fly Country.’ Investigation brought to light the curious fact that most of the 
wild animals—the buffalo, the koodoo, the wildebeeste—carried the trypanosomes 
in small numbers in their blood, and it was from them that the fly obtained the 
parasite. The wild animals act as a reservoir of the disease. The trypanosome 
seems to live in the blood of the wild animals without doing them any harm, just 
as the rat trypanosome lives in the blood of healthy rats; but when introduced 
into the blood of such domestic animals as the horse, the dog, or ox it gives rise 
to a rapidly fatal disease. The discovery that the wild animals act as a reservoir 
of the disease accounted for the curious fact that Tsetse-fly Disease disappears 
from a tract of country as soon as the wild animals are killed off or driven away. 
In 1895 the living trypanosome which causes the Tsetse-fly Disease was sent 
to England in the blood of living dogs, in order that it might be studied in the 
English laboratories. These trypanosomes have been kept alive ever since by 
passage from animal to animal, and have been sent all over Europe and America, 
so that our knowledge of this kind of blood parasite has rapidly grown. 
Koch, in a recent address, says that our knowledge of protozoal diseases is 
based on three great discoveries—that of the malarial parasite, by Laveran; of 
the Piroplasma bigeminum, the cause of Texas Fever or Redwater in cattle, by 
Smith ; and, lastly, this discovery of a trypanosome in Tsetse-fly Disease. 
We may therefore, I think, congratulate ourselves on the growth of our 
knowledge of this great stock disease during the last ten years. 
Since 1895 many other trypanosome diseases have been discovered in all parts 
of the world. The latest and most important of these is one which affects 
human beings, and is known as ‘ Sleeping Sickness.’ This ‘ Sleeping Sickness,’ which 
occurs on the West Coast of Africa, particularly in the basin of the Congo, has 
within the last few years spread eastward into Uganda, has already swept off 
some hundreds of thousands of victims, is spreading down the Nile, has spread all 
round the shores of Lake Victoria, and is still- spreading southward round Lakes 
Albert and Albert Edward. This disease is in all respects similar to the Nagana 
or 'T'setse-fly Disease of South Africa, except that it is caused by another species 
of trypanosome and carried from the sick to the healthy by means of another 
species of tsetse-fly—viz. the Glossina palpalis. 
I now throw on the screen a map of Africa, showing, as far as is known up to 
the present, the various fly districts, and you will see from this map that it is not 
