TRANSACTIONS OF SECTION I. 541 
at allimprobable that this human Tsetse-fly Disease may spread southward through 
the various fly districts to the Zambesi, and may even penetrate as far as the fly 
districts of the Transvaal and Zululand. 
I am sorry to say that, in spite of innumerable experiments directed towards 
the discovery of some method of vaccination or inoculation against these trypano- 
some diseases, nothing definite, up to the present time, has been discovered. At 
present there does not seem to be any likelihood that a serum can be prepared 
which will render animals immune to the Tsetse-fly Disease. In the same way it 
has also been found impossible, up to the present, to so modify the virulence of 
the trypanosome as to give rise to a modified, non-fatal form of the disease. 
Again, all attempts at discovering a medicine or drug which will have thepower of 
killing off the parasites within the animal organism, without at the same time 
killing the animal itself, have not as yet been successful, although some drugs, 
such as arsenic and certain aniline dyes (Ehrlich), have a very marked effect in 
prolonging the life of the animal. As this disease is fatal to almost every domestic 
animal it attacks, it seems very improbable that there is much chance of culti- 
vating an immune race of horses, dogs, or cattle which will be able to withstand 
the action of the parasite. It is quite evident that if an acquired immunity of 
this kind could be brought about, such a race of immune animals would now be 
found; but, as a matter of fact, there are no horses, dogs, or cattle in the ‘Fly 
Country.’ In other protozoal diseases, such as the Piroplasmata, this acquired 
imminity seems to come about fairly readily. 
To sum up, then, the increase in our knowledge of Tsetse-fly Disease during the 
last ten years, we may say that we have discovered the cause in the shape of the 
small blood parasite Trypanosoma; we have found that the reservoir of the disease 
exists in the wild animals, and that we can blot out this disease from any par- 
ticular tract of country by the simple expedient of destroying or driving away the 
wild animals. We still have no means of preventive inoculation or successful 
medicinal treatment in this disease. 
2. Trypanosomiasis of Cattle. 
This disease seems to be widespread over all South Africa. It cannot be said 
to be of much practical importance, as the cattle intected do not seem to be 
seriously affected by it. It is caused by a species of trypanosome remarkable for 
its large size, which was discovered by Dr. Theiler some years ago, and named 
T. theileri, 
Dr. Theiler states that it is conveyed from animal to animal by the common 
horse-tly, Hippabosca rufipes. 
‘ This, then, isa short account of the trypanosome diseases which affect South 
Africa. 
Of late years the T'setse-fly Disease has become of less practical importance to 
the Transvaal, from which it has practically disappeared. ‘This is due to the dis- 
appearance of the game, killed off by Rinderpest; but with the preservation and 
restoration of the reserves with big game the disease is certain to reappear. Why 
the fly should disappear with the gime is not known, 
B. Parasite unknown. 
I, Rinderpest. 
We now turn our attention to the important diseases of the second group. In 
these the parasites causing them are unknown—that is to say, no parasites can 
be detected by the microscope or by culture—but it is equally true that they must 
be present in the blood and fluids of the sick animals in some form or other. In 
all probability they are ultra-microscopic—too small to be seen with our present 
instruments. This is borne out by the fact that they are able to pass through the 
pores of porcelain filters, which keep back the smallest micro-organisms we are 
able to recognise. 
The first of the second group of diseases is Rinderpest, which has overrun and 
devastated South Africa within the last ten years, 
