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TRANSACTIONS OF SECTION I. 539 
But he found out that as the virus of Horse-sickness keeps its virulence for years, 
whilst the Piroplasma equi dies out in a short time, this danger could be avoided by 
keeping the Horse-sickness serum and virus for some time before using it. 
4. Malignant Jaundice of Dogs. 
This disease is most important to sportsmen or to importers of valuable dogs, 
as most of these are attacked sooner or later by this disease, and most of them 
succumb. It is also caused by a species of Piroplasma (Piroplasma canis), and is 
spread by the dog tick (Hcemophysalis leachit). 
Like Redwater and Biliary Fever, the blood of dogs which have recovered 
remains infective. 
The story of the tick infection is a curious one, and the credit of its discovery 
is due to Lounsbury. It is only in the adult stage that the tick is capable of 
producing the disease. It is therefore evident that the Piroplasma must remain 
latent in the egg, the larval and nymphal stages, and only attain activity in the 
adult stage. 
According to Theiler there exists a peculiay phenomenon which may be made 
use of to confer immunity. The blood of a dog which has recovered from this 
disease and has been hyper-immunised is, as mentioned above, capable of giving 
rise to the disease in a susceptible dog. Now, if serum be obtained from this 
blood and a quantity added to a small amount of the blood, this infected blood 
loses its infectivity and no disease results. 
IT. DISEASES CAUSED BY PARASITES BELONGING TO THE GENUS TRYPANOSOME. 
1. Nagana or Vsetse-fly Disease. 
We now come to the second group of diseases. These are also caused by 
blood parasites belonging to the same class of living things as the Piroplasma, but 
which are free organisms, swimming in the fluid part of the blood, and not 
contained in the red blood corpuscles, as are the others. 
The first of this group I would draw your attention to is that disease called 
Nagana or the Tsetse-fly Disease. 
This fly renders thousands of square miles of Africa uninhabitable. No horses, 
cattle, or dogs can venture, even for a day, into the so-called ‘Fly Country.’ Now 
what was our knowledge of this disease ten years agoP At that time it was 
thought that the tsetse-fly killed animals by injecting a poison into them, in the 
same way as a snake kills its prey. Nothing was known as to the nature of this 
poison in 1894, In 1895, on account of serious losses among the native cattle in 
Zululand from this plague, the then Governor of Natal and Zululand, Sir Walter 
Hely-Hutchinson, started the investigation of this disease. The result of this 
investigation was the discovery that Tsetse-fly Disease was not caused by a simple 
poison elaborated by the fly, as formerly believed, but that the cause of the disease 
was a minute blood parasite which gained entrance to the blood of the animals. 
This parasite is known by the name Trypanosoma, which signifies a screw-like body, 
Ten years ago two species only had attracted much attention—one living in the 
blood of healthy rats, discovered by Surgeon-Major Lewis in India; and the other, 
a trypanosome, found in the blood of horses and mules suffering from a disease 
known in India as ‘Surra.’ As the result of this investigation in Zululand, which 
lasted two years, it was proved that this trypanosome was undoubtedly the cause 
of the death of the horses and cattle struck by the fly, and that the tsetse-fly 
merely acted as a carrier of this blood parasite. 
Here is a representation of the trypanosome of Nagana on the screen. These 
trypanosomes consist of a single cell; are sinuous, worm-like creatures, provided 
with a macronucleus and a micronucleus, a long terminal flagellum, and a narrow 
fin-like membrane continuous with the flagellum and running the whole length 
of the body. When alive they are extremely rapid in their movements, constantly 
dashing about, and lashing the red blood corpuscles into motion with their 
flagellum, They swim equally well with either extremity in front. These 
