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DISTINCTION OF SPECIES 



A difficulty that confronts everyone who is 

 dealing with an unknown trypanosome is the question 

 of its identity with species already known. There are 

 many ways of attempting to solve this question. 



1. Morphology. Though it is frequently difficult 

 to distinguish pathogenic trypanosomes, e.g., T. brucei 

 and T. evansi, yet some can be readily distinguished ; 

 e.g., T. equinum of Mai de Caderas can be easily 

 distinguished by its extremely minute blepharoplast, 

 and similar differences exist in varying degrees among 

 morphologically similar trypanosomes. 



In making such comparisons the trypanosomes 

 must always be taken from the same kind of animals 

 e.g., guinea-pig. 



2. Pathogenicity. T. theileri, apart . from its 

 morphological characters, is distinguished by the fact 

 that it is specific for cattle, i.e., it cannot be inoculated 

 into other animals ; forming with T. lewisi (specific for 

 rats) Koch's two specific trypanosomes. On the 

 other hand most pathogenic trypanosomes (non- 

 specific, Koch) can be inoculated into a variety of 

 animals. A comparison of the results got by these 

 inoculations is used as a means of establishing the 

 identity of two trypanosomes, e.g., the trypanosomes 

 of human trypanosomiasis and sleeping sickness have 

 identical effects on animals, and hence are judged to 

 be identical. Again, T. equiperdum, though closely 

 resembling T. brucei is easily distinguished from it 

 by the fact that cattle are refractory to it. This 

 method, however, has its drawbacks ; as two trypano- 

 somes, almost certainly identical, coming from the 

 same locality and from 'among the same herd of 

 animals may differ so considerably in virulence, that 



