TRYPANOSOMA 67 



The following genera will be considered : 



Trypanosoma with an undulating membrane along the length 

 of the body. 



Crithidia with a less well-developed undulating membrane 

 anteriorly (see fig. 49). 



Herpetomonas including the so-called Leptomonas, with anterior 

 free flagellum only, and no undulating membrane. 



Leishmania non-flagellate forms in mammalian blood, flagel- 

 late herpetomonad stages in culture, probably occurring 

 naturally in Arthropods. 



Genus. Trypanosoma, Gruby, 1843. 



The members of the genus possess a single flagellum, which 

 arises posteriorly, adjacent to a blepharoplast or kinetic nucleus. The 

 flagellum forms a margin to an undulating membrane, and may 

 or may not be continued beyond the body as a free flagellum. 

 Many species are parasitic in vertebrate blood and in the digestive 

 tracts of insects. 



HISTORICAL. 



The history of blood flagellates goes back to the year 1841, in which Valentin 

 discovered in the blood of a brook-trout (Salmo fario L.) minute bodies, from 7 m 

 to 13 /a. in length, with active movements and presenting marked changes in form. 

 Valentin considered the parasite a new species of the old genus Proteus or 

 Amoeba, Ehrbg. This announcement led Gluge (1842) to publish a similar discovery 

 he had made in frog's blood. The latter forms were called by Mayer (1843) Amoeba 

 rotatoria, Paramcecium loricatum and P. costatum, while Gruby (1843) called them 

 Trypanosoma sanguinis. 1 Later it was discovered that similar organisms occurred 

 also in the blood of birds (Wedl (1850), Danilewsky) and of mammals. Gros (1845) 

 found them in the mouse and mole, Chaussat (1850) in the house rat, Lewis (1879) in 

 the Indian rat, Wittich (1881) in the hamster. D'anilewsky (1886-89) and Chalach- 

 nikow (1888) investigated the structure and division of trypanosomes. 



In the case of all these forms, there was no discussion as to a pathogenic 

 influence on the host. Opinion, however, as to the action of trypanosomes 

 changed when, in 1880, Evans found flagellates in the blood of horses in India 

 that suffered from a disease endemic there called " surra," and associated 

 the parasites with the disease. Steel and Evans were successful in transmitting 

 the parasites first known as Spirocktzta evansi, Steel, then as Trichotnonas 

 evansi, Crookshank, and finally as Trypanosoma evansi to dogs, mules and horses. 

 They recognized that the above mentioned flagellates in the blood of the experi- 

 mental animals were the causal agents of the disease. 



From that time there was a considerable increase in the literature, the 

 contents of which have been summarized by Laveran and Blanchard. In 1894 

 Rouget discovered trypanosomes in the blood of African horses that suffer 



1 Gruby's generic name is generally accepted. Still others have been used, e.g., Undulina* 

 Ray Lankester, Globtdaria Wedl, Paramecioides Grassi, Trypanomonas Danilewsky, 

 H&matomonas Mitrophanow. 



