PRESIDENT S ADDRESS. 



Within the last ten months Bruce has made a further inter- 

 esting announcement in connection with the trypanosome disease 

 of Nyassaland, where he is at present working. You will 

 remember that cases of sleeping sickness have occurred there, and 

 a trypanosoma was detected and described under the name of 

 Trypanosoma rhodesiense, and Bruce now writes me saying that 

 as this parasite is different to Trypanosoma Gambiense, the 

 disease cannot be called sleeping sickness. This statement will 

 help to explain many observations hitherto thought contrary to 

 our knowledge of that disease. 



The layman is, as a rule, satisfied when he knows that a 

 disease is carried by an insect; he then understands at least the 

 distribution and the spread of it. An explanation of the real 

 meaning of the observations must, however, be given in order to 

 understand the phenomena from a biological point of view. 

 What are the trypanosomes, and what is meant by their passage 

 from a mammal into a fly, and vice versa? 



Trypanosomes are small animals of the protozoon tribe with a 

 definite life-cycle only recognised in recent times. A sexual 

 reproduction alternates with an asexual one, the former taking 

 place within the body of the fly, the latter within the body of the 

 reservoir, men or animals. The asexual multiplication within 

 the animal ensures the propagation of the species, an infected 

 animal offering plenty of opportunity for flies partaking of its 

 blood, and subsequently the parasites present in the fly undergo 

 a process of renovation. That such is the case has recently been 

 shown in the laboratories in Europe.. When animals suffering 

 from certain protozoon diseases are treated with certain drugs, 

 some of. the parasites become drug-resistant, but they lose this 

 acquired quality as soon as they have passed through their host, 

 that is, undergone a sexual reproduction. When explaining the 

 life-cycle of these organisms to interested people, the question is 

 usually put to me, " Where do they come from ? The disease 

 being only of recent occurrence, have they always been present, 

 or do they spring up suddenly, and why ? " From a South 

 African point of view this is quite a natural question. The 

 diseases are old ones ; as already explained before, they are only 

 new to science, and we cannot imagine that they have originated 

 within historical times. Considering them in the light of evo- 

 lution, we must accept the idea that at a far-removed period 

 there must have been a beginning. Analogies with other para- 

 sites in other flies will demonstrate such a possibility. If we 

 kill a common house-fly and put the contents of its stomach under 

 the microscope, we shall, in a good many cases, detect a parasite 

 called Crithidium, a flagellate resembling the trypanosoma. They 

 are present in a good many species of flies, particularly in blood- 

 sucking flies, and this being so, it is not difficult to understand 

 how such a parasite, accustomed to a constant blood diet in the 

 body of the fly, could find its way into the body of the animal, 

 and from there back again into the fly. The explanation of the 



