335 
Is admitted to he a ‘jjood species,’ ancl solely from its morj^holo^y ; 
T. iquimm and T. theilert, the former more especially, are also 
fcnstituted largely from their unique appearance in the blood. 
A cbnician may subdivide the iliscascs due to trypanosomes on 
svioptomatological or epidemiological grounds: and a pathologist 
may add to these the results of liis observations on animals experi¬ 
mentally infected. Here again absolute distinction between any two 
species ma\' be imjxissible, even tliough it be l<nown that the 
morphology of each is markedly different. Thus the experimental 
disease, or the ‘ animal reactions’ due to I . evnnsi and 1 . dimorfhon^ 
showvery little variation ui most Mammals; yet these organisms are 
clearly distinguishable on morphologir.il grounds. Again, it would 
be a matter of the utmost difficulty to stale specifically that 
T. ^ambiense was not the same as / . crrtw.r/, if only dead organisms 
were available, but if ex[)crinicntal animal reactions arc considered, 
and the natural disease due to each be observed, they can be most 
strikingly separated. 
However larking in conformity to Zoological rules, and however 
imperfect and crude, it is jxrssible, by adoiiting a combination of the 
results given us by morphological and pathological studies, to 
constitute various groups of mammalian trypanosomes, which to a 
worker removed from such facilities as exist in the research centres of 
Europe are, to our mind, helpful. An observer in the field may place 
a detected trypanosome, tentatively, in one of the classes with a 
minimum amount of work, and since he will be in possession of only 
a modicum of research cquijiment and a limited stock of experimental 
animals, he will be in a jjosition to utilise these to their best advantage, 
and by adopting a certain degree of uniformity can bring his 
observations into line with all work previously carried out on the 
olass of organisms to which his own approximates. Absolute 
(iifferentiation of closely related trypanosomes is quite impossible to 
such a worker; a rigorous and critical morphological comparison must 
Ee effected, and final diagnosis will rest upon the result of this and 
that of ' cross-inoculation ' into animals believed to be immunise 
against the organisms with which comparison is being made. 
For such work ‘types’ of known and approved origin must 
Eand, as well as the necessary animals for cross-inoculation 
remain the work of an acknowledged centre, assuming e 
