2Q8 AFRICAN PATHOGENIC TRYPANOSOMES [CH. 



in the case of the numerous cattle trypanosomes of Africa, and 

 at the present time there is no simple method by which the 

 different varieties can be distinguished with any certainty. 

 In some cases the morphology is sufficiently distinctive, but in 

 most cases the trypanosomes are chiefly distinguished by their 

 biological characters, and these are often very difficult to observe 

 even in well equipped laboratories. In every case, there- 

 fore, species should be distinguished as much as possible by 

 morphological characters, for the present practice of giving 

 specific names to merely " physiological varieties " is of 

 questionable value. 



In the following table we have adopted Laveran and 

 Mesnil's method of sub-dividing trypanosomes into three groups, 

 according to the presence or absence of a free flagellum, or 

 those strains in which both forms occur. It has been found 

 necessary to omit many so-called species that have been in- 

 sufficiently described, and whose identification is very uncertain, 

 if not impossible. 



Key to the pathogenic trypanosomes of Africa. 



A. Trypanosomes in which the flagellum always possesses 

 a free part anteriorly. 



f Living trypanosome extremely active, frequently darting across the field 

 of the microscope. Dogs, monkeys, rats and mice all refractory to 



1 -{ infection ; ruminants and horses susceptible 



= cazalboui, Laveran ( =vivax, Bruce etc. nee Ziemann). 

 I Dogs, rats and mice susceptible to infection . . . . . . 2. 



f Monkeys and ruminants more or less refractory to infection. Horses 



2 { susceptible .. , = equiperdum, Doflein. 



L Monkeys and ruminants susceptible to infection . . ..*.... =3 



f Parasite more or less dimorphic . . =brucei, Plimmer and Bradford. 



3 j f evansi, Steel. 



i j evansi var. mbori, Laveran. 



L Parasite monomorphic .... <j togolensg> Mesnil and Brimont . 



(.soudanense, Laveran. 



The latter four trypanosomes are distinguished by their cross immunity 

 reactions. 



