72 THE ANIMAL PARASITES OF MAN 



the flagellum free (e.g., T. congolense), while the third group included 

 forms some members of which have free flagella, while others have 

 not (e.g., T. gauibiense). Bruce 1 (1914) and Yorke and Blacklock 2 

 (1914) have also devised classifications. 



Resting stages of some trypanosomes have been found in the 

 internal organs of their vertebrate hosts. The formation of these 

 oval, Leishmania-like bodies will be noted in individual cases later. 

 Similar small oval bodies form an important phase in the life-history 

 of T. cruzi, which multiplies normally by multiple fission or schizogony 

 into these oval, daughter elements, and not by binary longitudinal 

 fission in the circulating blood. 



Polymorphism in trypanosomes (e.g., T. gauibiense, T. rhodesiense) 

 is now interpreted as a phenomenon resulting from growth and 

 division. 3 Long, thin forms are those about to divide. Fully mature 

 forms are shorter and broader. Various intermediate types occur and 

 represent growth forms. Formerly, polymorphism was interpreted in 

 terms of sex, thin forms being regarded as males, broad forms as 

 females, while the intermediate types were termed indifferent. Con- 

 jugation was not observed, and there is no evidence in support of 

 the sexual interpretation. 



The transmission of trypanosomes from one vertebrate host to 

 another is usually accomplished by the intermediation of some biting 

 arthropod in the case of terrestrial animals, while leeches are usually 

 considered to act as transmitters in the case of the trypanosomes 

 occurring in aquatic animals. Developmental phases of the life- 

 histories of trypanosomes occur in the invertebrate transmitters, and 

 will be considered in individual cases. 



Trypanosoma gambiense, Button, 1902. 



Syn. : Trypanosoma hominis, Manson, 1903. Trypanosoma nepveui, Sambon, 1903. 

 l^rypanosoma castellanii, Kruse, 1903. Trypanosoma ugandense, Castellani, 

 1903. Trypanosoma fordii, Maxwell Adams. 



In vertebrate blood Trypanosoma gambiense is polymorphic, for 

 long, thin forms may be seen in contrast with short, stumpy forms, 

 as well as intermediate forms (fig. 29, a c). This polymorphism has 

 been interpreted in terms of sex, especially by German investigators, 

 following Schaudinn (see above). However, there is no evidence of 

 conjugation, and the polymorphic forms are more easily interpreted 

 in terms of growth and division, for the long thin forms are potential 

 dividing organisms, and the stumpy or short parasites, with little or 

 no free flagellum, are the adult individuals. 



1 Trans. Soc. 7rop. Med. cSr" Hyg., viii, p. I. 



2 Annals Trop. Med. and Parasitol., viii, p. I. 



3 Robertson (1912), Proc. Roy. Soc., B, Ixxxv, p. 527. 



