THE PRESIDENT'S ADDRESS. 441 



may be stated in two propositions, one positive, one negative ; 

 first premising that by a malarial infection is meant a new 

 infection, not a relapse in a person previously infected. 



1. Malaria can be and is conveyed from sick to healthy 

 persons by the agency of mosquitoes. 



2. Malarial infection is not known to take place by any other 

 method. 



Experiments further showed, as I have mentioned already, the 

 very remarkable fact that avian malaria can only be transmitted 

 by Culicine mosquitoes, and human malaria only by Anopheline* 

 If human blood containing the parasite be taken up by a Ctdex, 

 the parasite cannot develop, but is digested up, along with the 

 blood. The same thing happens to the parasite of avian malaria 

 when taken up by an Anoj)heles. 



Following on these experimental discoveries, the development 

 of the parasite was studied microscopically in all countries by a 

 great number of observers, amongst whom we may mention 

 especially Grassi in Italy and Schaudinn in Germany. By their 

 combined labours the complete life-history of the parasite ha> 

 been worked out in the greatest detail, revealing one of the most 

 fascinating chapters in natural history. 



[An account was then given of the development of the malarial 

 parasite, illustrated by a diagram.] 



My second example, sleeping sickness, is also a disease that has 

 been long known, though without attracting, until recently, so 

 much attention as malaria. It was first observed in the West 

 Indies in negro slaves imported from the west coast of Africa, 

 the region in which it appears to be endemic. It was observed 

 that the negroes suffering from it were not infectious, and that 

 the disease did not spread to others — a fact easily explained by 

 what is now known about the transmission of sleeping sickne». 

 namely, that it is effected by fiies of the genus Glossina, commonly 

 known as tsetse-flies, which are confined at the present time to 

 the African continent. 



Of recent years this previously obscure disease has forced itself 

 on the public attention by its having spread from its native 

 haunts on the west of Africa and invaded regions previously free 

 from its presence. In our Protectorate of Uganda, in particular, 

 it has caused terrible mortality, completely extirpating the 

 natives in some parts, and numbering also many Europeans 



