324 TRYPANOSOMA RHODESIENSE [CH. 



of this disease in one small region, followed by such a rapid 

 spread, can only be explained on the supposition that it is an 

 entirely new form of sleeping sickness. Moreover, its extremely 

 deadly effect on its vertebrate host, man, is further evidence 

 in support of the same view. 



T. rhodesiense is remarkably pathogenic to the majority of 

 experimental animals, the duration of life of monkeys infected 

 with this species being only about 8 to 14 days, as compared 

 with 27 to 149 days in the case of T. gambiense. It is evident, 

 therefore, that this new trypanosome is extraordinarily virulent, 

 and it is also very resistant to treatment, atoxyl apparently 

 having no effect on it. 



In man the course of the disease is much more rapid than 

 in the case of ordinary sleeping sickness {T. gambiense) and 

 death usually takes place within three or four months of 

 infection. 



At present T. rhodesiense is restricted to Southern Nyasaland, 

 North-Eastern Rhodesia, especially in the Luangwa Valley, and 

 Portuguese East Africa, but it seems to be extending its range 

 and unless effective preventive measures are discovered there 

 is reason to fear that it may give rise throughout Africa to an 

 epidemic, besides which the ravages of gambiense would appear 

 almost mild in comparison. 



Morphology of the parasite. T. rhodesiense in most respects 

 resembles T. gambiense, but is characterised by the occurrence 

 of stout or stumpy forms in which some have the trophonucleus 

 at the posterior end. Stephens and Fantham give the following 

 account of the parasite : " Rats inoculated with this Rhodesian 

 strain usually shew a few long thin trypanosomes in the 

 peripheral blood in about three days. The stumpy forms of 

 trypanosomes with the trophonucleus posterior appear about 

 the fifth or sixth day and from this time onwards somewhat 

 increase in number up to the seventh or eleventh day. They 

 then form about six per cent, of the trypanosomes present, but 

 may decrease again, varying from day to day." 



The dimensions of stumpy forms with a posterior tropho- 

 nucleus vary from 17 to 21 microns in length by 2 to 3 

 microns in breadth. There is a well-marked kinetonucleus 



