4 PRESIDENTS ADDRESS. 



any investigations had been made by experts. The farmers' 

 interpretations led to certain conclusions which had become more 

 or less common knowledge ; they were carried down from 

 generation to generation, and accepted as old-establishes ! 

 truisms. In the light of modern knowledge many of these 

 opinions no longer held good, and it appeared to many an old 

 farmer almost a blasphemy to abandon the notions which had 

 directed him in all his undertakings on his farm since the days of 

 his childhood. There was a time, and perhaps still is, when the 

 experts were looked upon with suspicion. I cannot help sym- 

 pathising with this people, but I have no sympathy with those of 

 whom one would expect that their education would enable them 

 to understand logical and scientific reasoning. As I said, the 

 observations were, in the majority of instances, correct, and I 

 have no hesitation in saying that in most of my work, first of all 

 I relied on the information given by the sons of the soil. I have 

 done so up to the present time, and I shall not fail to do so again 

 when opportunity occurs. It is true that much information is 

 wrapped up with personal opinion, and even a layman requires 

 his own theories to explain his observations, but a careful 

 analysis usually helps to separate the two. My paper will also 

 show that these so-called empiric notions have given valuable 

 assistance to the unbiassed scientific worker. 



Now let us look into the diseases of South Africa, which 

 everyone at one time thought to be typical of this sub-continent. 

 To begin with, I will mention the "tsetse fly" disease. This 

 may perhaps not be the oldest known, but it is a classical one. 

 and was already mentioned in the writings of the great Living- 

 stone. This one has been well studied, and at the present time 

 it still forms the basis of many theoretical speculations of a far- 

 reaching nature. The name of a distinguished scientist well 

 known in South Africa, Sir David Bruce, is connected with it. 

 Bruce started his work in Zululand, in 1895, through the protec- 

 tion of a man much devoted to science, the then Governor, Sir 

 Walter Hely Hutchinson ; his name will always be remembered 

 as a past President of our Association, and as a friend of every 

 man engaged in scientific investigations and research. In the 

 blood of an infected animal suffering from a disease which the 

 Zulus called Nagana, Bruce found a micro-organism not pre- 

 viously seen in any part of Africa, a parasite belonging to the 

 group of trypanosomes, and now named after its discoverer. 

 The credit is due to Bruce not so much for finding this parasite, 

 which in our days seems but a trivial thing, but for showing the 

 connection between these parasites, the game of the country in 

 which they were living, and from which they were transmitted 

 to healthy stock by means of the tsetse fly, and in understanding 

 from the very beginning its true meaning and importance. This 

 led to the conception of the " reservoir of the virus," meaning 

 that the germs of a disease are present in some animals where 

 they live in a state of symbiosis, not causing any disease, and 



