298 



SCIENCE. 



[N. S. Vol. XXII. No. 558. 



blood of sucli domestic animals as the horse, 

 the dog or ox it gives rise to a rapidly fatal 

 disease. The discovery that the wild ani- 

 mals act as a reservoir of the disease ac- 

 counted 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 Eng- 

 lish 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 

 Mgeminum, 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 dis- 

 eases 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 al- 

 ready swept off some hundreds of thousands 

 of victims, is spreading down the Nile, has 

 spread all round the shores of Lake Vic- 

 toria, and is still spreading southward 

 round Lakes Albert and Albert Edward. 

 This disease is in all respects similar to the 



nagana or tsetse-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 at 

 all improbable 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 dis- 

 tricts of the Transvaal and Zululand. 



I am sorry to say that, in spite of innu- 

 merable experiments directed towards the 

 discovery of some method of vaccination or 

 inoculation against these trypanosome dis- 

 eases, nothing deflnite, 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 discov- 

 ering a medicine or drug which will have 

 the power 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 cultivating 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 ani- 

 mals would now be found ; but, as a matter 



