PRESIDENTIAL ADDRESS. 15 



may perhaps take Koch's own words that " no doubt can 

 longer exist as to the specific action of the drug." The 

 question is, will the effect be permanent? — and this, time 

 alone can show. If the answer is affirmative think of the 

 mass of human misery and suffering thus averted, and 

 think' of the fertile lands thus made habitable. 



The Tsetse fly which has been longest known, was the 

 reputed cause of the terrible horse and cattle sickness which 

 decimated the herds of imported horses and cattle in South 

 Africa, and has had decisive influence on colonisation and 

 campaigns. We now know that the real cause is 

 not the fly, but something carried by the fly. This 

 is believed to be Trypanosoma brueei, called 

 after its discoverer, Colonel David Bruce, who showed 

 that the Tsetse fly really conveyed the Trypanosome from 

 the native big game — zebras, antelopes, and possibly buf- 

 faloes — to the imported animals. The native animals had 

 become tolerant of it — it multiplies in their blood too, but 

 does not kill or even injure them. They of course are the 

 descendants of animals which had resisted the attacks — 

 all those that could not having been wiped out by natural 

 selection. In precisely the same way the children of native 

 negroes are tolerant of the malaria organism. More 

 recently the identity of the really pathogenic organism 

 in this disease has been again placed in doubt, but it 

 is perhaps early as yet to say much more about it. In 

 any case, however, the subject has a certain interest to 

 ourselves, for there is a horse sickness in India called 

 "Surra," in which a Trypanosome is found in the blood, 

 and which is similar to if not identical with the corres- 

 ponding disease in South Africa. But Surra is now quite 

 prevalent in the Phillipines and parts of Malaya, 

 with which we have a growing commerce. If by any 

 chance the disease is transferred to Australia the losses to 



