TRYPANOSOMA 



395 



that they may become pathogenic; and that this change, though 

 merely at first chemical, may subsequently become structural. 



The researches of O'Farrell, Fantham, and Porter, already referred 

 to under the Herpetomoninae, seem to indicate that the original try- 

 panosomes were parasites of such invertebrates as Annulates, 

 Arachnids, and Hexapoda, from which they spread to vertebrates. 



With regard to man, it would appear as though his infection was of 

 comparatively recent date, and that in him and in the tsetse-flies 

 which infect him the adaptation of the trypanosomes to the new 

 environments is not yet complete, and therefore the differential 

 characters of the various species infecting him have not yet become 

 completely crystaUized. 



It therefore appears to us that a natural division of the numerous 

 species of trypanosomes would be into— 



A. Trypanosomes infecting invertebrata : — 



L Trypanosomes of Hirudinea. 

 II. Trypanosomes of Arachnida. 

 III. Trypanosomes of Hexapoda. 



B. Trypanosomes infecting cold-blooded vertebrates :• — 



I. Trypanosomes of Pisces. 

 II. Trypanosomes of Amphibia. 

 III. Trypanosomes of Reptilia. 



C. Trypanosomes infecting warm-blooded vertebrates: — 



I. Trypanosomes of Aves. 

 II. Trypanosomes of Mammalia. 



It is not our purpose to write accounts of all known trypanosomes, 

 but merely those which infect man, and to sketchily describe some 

 of those which produce disease in the mammalia, and to draw atten- 

 tion to others which can be classified in the series of divisions given 

 above. 



With regard to the trypanosomes of mammals, it appears to us, 

 from an evolutionary point of view, to be correct to divide them into 

 two sections— viz. : — 



A. Non-pathogenic mammalian trypanosomes. 



B. Pathogenic mammalian trypanosomes. 



As it is the last section only with which tropical medicine is con- 

 cerned, we shall restrict our further remarks on classification until 

 we come to these organisms. 



A New Classification. — Although, for purposes of general infor- 

 mation, we have given the usual classification, still, it must be 

 obvious even to the casual reader that the genus Trypanosoma com- 

 prises an enormous number of species, some of which are of very, 

 diverse form. 



JWe feel that the time has arrived in which to bring forward a fuller 

 and more useful classification, based upon morphological and 

 physiological characters, especially as classifications have been 



