PRESIDENT S ADDRESS. 5 



from which they are obtained by the blood-sucking insects and 

 transmitted to the susceptible animal. The notion of the old 

 hunters of the country that the fly was almost constantly asso- 

 ciated with the buffalo did not explain the mystery of the home 

 of the disease, although it was known at that time that the bite 

 of -the flies was succeeded by nagcma; Bruce explained it, how- 

 evr. by the discovery of the parasite. This fact, once established, 

 formed the clue for understanding many other diseases of a 

 similar nature, and in particular it fostered the study of human 

 malaria. Once it had been realised that in this disease the blood 

 parasite was a protozoon. the investigations received a great 

 impetus by the new views of nagana and its connection with the 

 tsetse fly. The knowledge gained from the observations in Zulu- 

 land had still a more far-reaching effect. It was the key to 

 other investigations which led to one of the most brilliant dis- 

 coveries of recent times, to the discovery of the cause of sleeping 

 sickness. The history, as related to me by Bruce, is particularly 

 interesting, and it shows how quickly results may be obtained 

 when theoretical deductions are thoroughly grasped and under- 

 stood. The Royal Society sent Bruce to Uganda to investigate 

 sleeping sickness which, as you will remember, killed thousands 

 of Natives and threatened the destruction of the population of 

 the Lake country. It had already been the object of investiga- 

 tions, but without any satisactory results. One of the men who 

 thought that he had finished his work — his name is of no concern 

 at present — considered he had found the cause in some bacterium 

 which he had isolated from the brain of dead people. He met 

 Bruce on his arrival, and in discussing his finding with my 

 friend, quite casually mentioned that he had seen a trypanosoma 

 in the blood of some of the patients, a parasite which by that 

 time had already been known in Western Africa under the name 

 of Trypanosoma Gambiense. It was not connected with any 

 definite ailment, and the disease was simply called the trypano- 

 soma fever. " Like a flash of lightning it went through my 

 mind." Bruce told me, " that this parasite must be the cause of 

 sleeping sickness and nothing else, and that if such was the case, 

 then it must be transmitted by a fly." Bruce was right. His 

 theoretical deductions, based on his previous observations, led 

 him immediately to the right conclusions. 



Sleeping sickness was found to be the human tsetse fly 

 disease ; the fly was found to belong to the same genus as that of 

 Zululand, vis., a Ghssina, in this particular instance Glossina 

 palpalis. This being so, the further deduction that there must be 

 a reservoir for the trypanosoma had to be considered. In the 

 first instance it was found that men suffering in a mild degree 

 from the so-called trypanosoma fever constituted that reservoir, 

 and only within the last few years another Commission sent out 

 by the Royal Society, and again led by Sir David Bruce, estab- 

 lished the fact that animals, particularly antelopes, could also 

 act as such reservoirs. 



