458 FAMILY: TRYPANOSOMIDiE 



Group A. — Trypanosomes which develop in the posterior station in 

 the invertebrate: 



I. Trypanosomes of rodents, Cheiroptera, Insectivora, Edentata, 

 monkeys. 



II. The trypanosome of man in South America, T. cruzi. 



III. Non-pathogenic trypanosomes transmitted by species of Tabanus, 

 Melophagus, or other blood-sucking Arthropoda, including the 

 large forms from cattle, sheep, and antelopes. 



Group B. — Trypanosomes which develop in the anterior station in the 

 invertebrate or have become secondarily adapted to direct passage from 

 vertebrate to vertebrate: 



I. Pathogenic trypanosomes transmitted by blood-sucking Arthro- 

 poda. 



II. Pathogenic trypanosomes secondarily adapted to direct passage 

 from vertebrate to vertebrate. 



III. Trypanosomes of birds (?). 



IV. Trypanosomes of land reptiles (?). 



V. Trypanosomes of aquatic vertebrates transmitted by leeches: 



1. Trypanosomes of aquatic reptiles. 



2. Trypanosomes of amphibia. 



3. Trypanosomes of fish. 



The pathogenic forms are those which produce disease in man and 

 domestic animals, but these cannot be regarded as the natural hosts. 

 In Africa, the pathogenic forms are naturally parasitic in the wild game, 

 where they are relatively non-pathogenic. They only become pathogenic 

 when inoculated into susceptible animals which have not developed a 

 relative immunity as a result of exposure for many generations. The 

 virulence of T. lewisi, which under natural conditions is quite harmless, 

 may be increased till it becomes definitely pathogenic, and T. inopinatum, 

 harmless for the African frogs, is pathogenic for those of France. The 

 pathogenic trypanosomes, however, form a convenient group, and are 

 transmitted in most cases by species of Glossina in Africa. There are 

 some pathogenic trypanosomes, however, in the transmission of which the 

 tsetse fly can play no part, as, for instance, T. evansi of surra and 

 T. equinum of mal de Caderas, which occur in countries where tsetse flies 

 are not found. In these cases other biting flies of the genus Tabanus 

 and its allies fulfil the role. As regards Trypanosotna equiperdum, its 

 affinities are undoubtedly with the trypanosomes of the pathogenic group. 

 It appears that its capacity of passing directly from vertebrate to verte- 

 brate has been secondarily acquired as a result of the situation of its 



