334 
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., 7 ". brucei 
and T. evansi, yet some can be readily distinguished ; 
e.g., 7 *. 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. — 7 ". 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 7 ". hrucei 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 
