SLEEPING SICKNESS. 331 



The position, then, is as follows. We have in Ehodesia and 

 Nyasaland a very virulent form of trypanosomiasis, carried by a 

 Glossina which has a wide local distribution and which is a much 

 more persistent biter than G.palpcdis, and, further, a considerable 

 percentage of the game is estimated to be infected by T. rho- 

 desiense. If this be really a new disease, it would seem that the 

 native population is faced with an epidemic beside which that 

 in Uganda would be a mere circumstance, and the most drastic 

 remedies that youthful enthusiasm can devise would appear to be 

 j ustified . 



On the other hand, we have to consider that the disease has 

 been known to exist in this area for nearly five years and has 

 probably been there a good deal longer ; for we can hardly be 

 asked to believe that by a remarkable coincidence Trypanosoma 

 rhodesiense chanced to be discovered at the precise moment of 

 its origin. Yet, in spite of the presence of these factors making 

 for the rapid development of a severe epidemic during all these 

 years, nothing of the kind has happened ; nor have we any real 

 reason to suppose that an epidemic is imminent. The evidence, 

 such as it is, seems to indicate that we are dealing with an endemic 

 disease, which is not likely to become worse if the present 

 conditions are mairjtained. And while further expeiimental 

 investigations should certainly be carried on, there is no justifica- 

 tion for anything in the way of panic legislation. 



Professor E. A. MINCHIN, M.A., F.R.S., F.L.S., V.P.Z.S., 

 said that in Dr. Yorke's paper he had heard nothing to criticise 

 or controvert, so far as statements of fact were concerned. The 

 two African trypanosomes deadly to man, namely Trypa'nosom.a 

 gambiense and T. 7'hodesiense, were members of a large group of 

 trypanosomes which was typified by the well-known T. brucei, 

 and might therefore be called the brucei-growp. There could be 

 hardly any doubt, in the present state of knowledge, but that the 

 brucei-group of trypanosomes was one which was primitively 

 parasitic upon wild ungulates, and that many species had been 

 carried secondarily by the agency of biting ilies to other verte- 

 brate hosts, in which they had been able to maintain themselves. 

 The fact that the trypanosomes of this group were harmless to 

 the wild ungulates but deadly to other animals showed that the 

 former were their natural hosts. Thus, T. gambiense and 1\ rho- 

 desiense were harmless to antelopes but deadly to man ; T. brucei 

 was harmless to wild ungulates but very deadly to domesticated 

 horses, cattle, or dogs. This conclusion did not apply, however, 

 to the human trypanosome of Brazil, T. cruzi, nor to cattle try- 

 panosomes of the theileri-type, forms which were quite distinct 

 from the brucei group. 



While a,greeing with Dr. Yorke on matters of fact, Prof. Minchin 

 thought that in the present state of our knowledge the utmost 

 caution should be exercised in putting into practice administrativ^e 

 measures based upon the data so far established. The inte*'- 



22* 



