340 TRYPANOSOMA VIVAX [CH. 



Trypanosoma vivax Ziemann, 1905. 



In 1905, Ziemann described under the name of T. vivax a 

 trypanosome occurring in the blood of cattle, sheep, and goats 

 in the Cameroons. The symptoms of the disease it produces 

 are almost identical with those of Souma, and moreover, in 

 its morphology, T. vivax closely resembles cazalhoui. But 

 Ziemann definitely states that rats are susceptible to T. vivax, 

 eight of them dying from the infection after eight, nine and 

 eleven days. Also a dog and a pig both shewed a temporary 

 infection. On the other hand, rats are absolutely refractory 

 to T. cazalhoui and this constitutes a method of distinguishing 

 the two. 



Bagshawe has called attention to the resemblance between 

 the two forms, and inclines to consider them as constituting a 

 single species. This view has been opposed by Laveran, and 

 certainly as long as " species " of trypanosomes are distin- 

 guished mainly on the basis of cross-immunity reactions and 

 the susceptibility of laboratory animals, it is impossible to unite 

 two forms differing so markedly in the latter feature. 



Bruce and his colleagues on the basis of a microscopic exam- 

 ination of Ziemann's shdes came to the conclusion that T. 

 cazalhoui Laveran was synonymous with T. vivax Ziemann. 

 Accordingly throughout their reports they have employed the 

 latter name for a trypanosome which is undoubtedly identical 

 with the T. cazalhoui of the French and Belgian authors. A 

 careful comparison of Ziemann's original description with 

 the accounts of cazalhoui, shew that although very closely 

 related the two forms may be easily distinguished by their 

 respective animal reactions. Thus, all small laboratory animals 

 and the pig are refractory to cazalhoui, whereas rats are very 

 susceptible to vivax and die within eleven days ; also a dog and 

 a pig shewed a temporary infection. 



As rats as well as the other small experimental animals are 

 not susceptible to the Uganda virus, it is evident that the species 

 of that region, which has been referred to as T, vivax, should 

 be known correctly as cazalhoui. 



