■i^ president's address. 



winged gnat or mosquito {Anopheles), not, as lie had at first bupposed, ill 

 the common gnat or mosquito (Culex), and that if we can get rid of spot- 

 winged mosquitoes or avoid their attentions, or even only prevent them from 

 sucking the blood of malarial patients, we can lessen, or even abolish, malaria. 

 This great discovery was followed by another as to the production 

 of the deadly ' Nagana " horse and cattle disease in South Africa by a 

 screw-like, minute animal parasite, the Trypanosoma Brucei. The 

 Tsetze fly, which was already known in some way to produce this 

 disease, was found by Colonel David Bruce to do so by conveying by its 

 bite the Trypanosoma from wild big-game animals, to the domesticated 

 horses and cattle of the colonists. The discovery of the parasite and its 

 relation to the fly and the disease was as beautiful a piece of scientific 

 investigation as biologists have ever seen. A curious and very important 

 fact was discovered by Bruce— namely, that the native big game (zebras, 

 antelopes, and probably buffaloes), are tolerant of the parasite. The 

 Trypanosoma grows and multiplies in their blood, but does not kill them 

 or even injure them. It is only the unaccustomed introduced animals from 

 Europe which are poisoned by the chemical excreta of the Trypanosomes 

 and die in consequence. Hence the wild creatures — brought into a con- 

 dition of tolerance by natural selection and the dying out of those susceptible 

 to the poison — form a sort of ' reservoir ' of deadly Trypanosomes for the 

 Tsetze flies to carry into the blood of new-comers. The same phenomenon 

 of 'reservoir-hosts' (as I have elsewhere called them) has since been 

 observed in the case of malaria ; the children of the native blacks in 

 Africa and in other malarious regions are tolerant of the malarial 

 parasite, as many as 80 per cent, of children under ten being found to be 

 infected, and yet not suffering from the poison. This is not the same 

 thing as the immunity which consists in repulsion or destruction of the 

 parasite. 



The Trypanosomes have acquired a terrible notoriety within the last 

 four years, since another species, also carriefl by a Tsetze fly of another 

 species, has been discovered by Castellani in cases of sleeping sickness in 

 Uganda, and demonstrated by Colonel Bruce to be the cause of that awful 

 disease. Over 200,000 natives of Uganda have died from it within the 

 last five years. It is incurable, and, sad to relate, not only a certain number 

 of European employes have succumbed to it in tropical Africa, but a brave 

 young officer of the Army Medical Corps, Lieutenant TuUoch, has died 

 from the disease acquired by him in the course of an investigation of this 

 disease and its possible cure, which lie was carrying out, in association 

 with other men of science, on the Victoria Nyanza Lake in Central 

 Africa. Lieutenant TuUoch was sent out to this investigation by the 

 Royal Society of London, and I will venture to ask you to join that 

 body in sympathy for his friends, and admiration for him and the other 

 fourageous men who risk their lives in the endeavour to arrest disease. 



Trypanosomes are now being recognised in the most diverse regions 

 of the world as the cause of disease — new horse diseases in South America, 



