PROTOMONADINA 



347 



selves to the duct-wall in crithidia form. Here the development con- 

 tinues for 2-5 days and the flagellates finally transform themselves 

 into small trypanosomes which are now infective. These metacyclic 

 trypanosomes pass down through the ducts and hypopharynx. When 

 the fly bites a person, the trypanosomes enter the victim. In addition 

 to this so-called cyclic transmission, mechanical transmission may 

 take place. 



Trypanosoma gambiense is a pathogenic protozoan which causes 

 Gambian or Central African sleeping sickness. The disease occurs in, 



Fig. 143. a-d, Trypanosoma gambiense; e-h, T. rhodesiense, in stained 

 blood smears of experimental rats, X2300. An erythrocyte of rat is shown 

 for comparison, a, b, typical forms; c, d, division stages; e, f, typical forms; 

 g, h, post-nuclear forms. 



and confined to, central Africa within a zone on both sides of the 

 equator where the vectors, Glossina palpalis and G. tachinoides (on 

 the west coastal region) live. Many wild animals have been found 

 naturally infected by the organisms and are considered to be reser- 

 voir hosts. Among the domestic animals, the pigs appear to be one 

 of the most significant, as they themselves are said not to suffer from 

 infection. 



The chief lesions of infection are in the lymphatic glands and in 

 the central nervous system. In all cases, there is an extensive small- 



