THE H^MOFLAGELLATES. 175 



which are especially liable to suffer naturally from the various maladies 

 (Nagana, Surra, Dourine, etc.), while the latter condition is more often met 

 with in small Mammals which have been artificially inoculated with one or 

 other of those Trypanosomes. While, in this case, the disease is of an 

 acute character and rapidly fatal, in the former it is more chronic and lasts 

 much longer (often several months), with, however, nearly always the same 

 termination. Even when microscopical examination of the blood is unsuc- 

 cessful in finding the parasites, their presence in it is proved by the fact 

 that, after the injection of a small quantity into another more susceptible 

 host, the Trypanosomes soon appear in the blood of the latter. 



There is, moreover, often considerable variability (particularly in chronic 

 cases of Surra and Mai de Caderas, for example) with regard to the appear- 



d,- 



FlG. 5. — Trypanosoma equiperdum (of Dourine), in the 

 blood of a rat eight days after inoculation. a = parasites j b = 

 blood-corpuscles. (After Doflein.) 



ance and number of the parasites in the blood at any moment. Occasionally 

 and at irregular intervals, evidently following upon a period of multiplica- 

 tion, the Trypanosomes may be fairly numerous, their appearance often 

 (though not invariably) coinciding with an access of fever. At other times 

 they seem to vanish almost entirely from the peripheral circulation. Why, 

 exactly, this should be so is not certain. Some authorities attribute it to 

 the rise in temperature, as being unfavourable to the parasites; others 

 think it is due to the more potent operation of chemical and physiological 

 defensive agencies of the host at a higher temperature. It is supposed that 

 certain of the organisms, more resistant than the majority, and situated, 

 perhaps, in some more favourable region of tlie body, survive and give rise 

 later to a fresh succession of parasites in the blood. 



The main features of the illness show a general agreement, whichever 

 variety of trypanosomosis is considered ; one symptom may be more marked 

 than another in any particular disease, but a fundamental similarity in type 

 is usually noticeable — so much so that it was, for instance, a long time 



