PRESIDENTS ADDRESS. 7 



cycle of trypanosomes means, therefore, nothing else than a well- 

 adapted parasitism similar to many others existing in the animal 

 kingdom, and the mystery attached to them gives way to well- 

 established facts. 



There is another interesting point connected with the 

 discovery of the Zululand trypanosome which should be recorded 

 in these days, where details of research are easily forgotten 

 Bruce knew, from the tales Of the old hunters who took their 

 horses into the hunting fields, that horses dosed with arsenic- 

 did not so readily contract the disease. Having realised that the 

 trypanosome was the cause of nagana, Bruce put the treatment 

 to the test, and found that under the influence of arsenic the 

 parasite, temporarily disappeared out of the blood, but re- 

 appeared when the eff ts of the drug had passed over. As T 

 explained just now, the parasite had become arsenic-resistant, 

 and further treatment became useless, but nevertheless the life 

 of the animal was prolonged. This observation must be con- 

 sidered to be the commencement of the modern chemico-therapeu- 

 tical investigations, where the influence of a medicine on a 

 parasitic organism is studied microscopically, and which has 

 resulted in the discovery of Ehrlich's salvarsan for the treat- 

 ment of all - caused by spirochetes. After Rruce's 

 publication, Professor Laveran of Paris took up the control of 

 the arsenic treatment, which in the course of time was tried 

 repeatedly, and altered until the successful results were 

 obtained. I mention this as another example to show how 

 empiric observations can be turned to useful account by an 

 unbiassed scientific mind. 



The conditions of infection and transmission in trypano- 

 soma disease which I have explained somewhat in detail also 

 holds good, mutatis mutandis, in our common malarial fever of 

 men. I hope there are no people among this gathering who are 

 unaware that the malarial fever is transmitted by mosquitoes, 

 as it is a fact so well established that there is no room left for 

 any doubt. In this disease the mosquito is the host : the parasite, 

 called a Plasmodium, undergoes the cycle of development in the 

 body of the mosquito, a phenomenon which can be actually 

 observed under the microscope. Man represents the reservoir 

 for the virus, particularly the natives of malarial countries who, 

 as long a- they are children, harbour the parasite in their blood, 

 it would be quite natural to ask whether animals also act as 

 reservoirs. To this the reply is that such is not the case. There 

 are, however, parasites belonging to the same genus present in 

 ? good many species of our birds, particularly in finches; they 

 have al o been found in a squirrel, and they are frequently 

 found in bats and in some species of climbing apes. Since all 

 these animals live in trees, the enthusiastic evolutionist may 

 make a surmise as to the origin of human malaria at a very 

 remote time. Tt was through the study of the blood of para- 

 sites in birds in the first instance that all the light has been 



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