PHYLUM PROTOZOA 37 



In contrast with the non-pathogenic T. lewisi stand some other 

 species of the same genus which produce fatal diseases in man 

 and other animals in Africa and South America. T. gambiense 

 and T. rhodesiense are the organisms responsible for the true 

 sleeping sickness in man. A single genus of fly known as the tsetse 

 fly (Glossina) transmits the trypanosomes to man. Rhodesian 

 sleeping sickness (transmitted by Glossina morsitans) is more 

 virulent than the Gambian variety (carried by G. palpalis). One 

 of the great difficulties experienced in control measures is the fact 

 that the trypanosomes seem to live normally in the bodies of ante- 

 lope and other game animals which thus serve as reservoirs for the 

 spread of the disease. When the 

 tsetse fly sucks the blood of an 

 infected person, the trypanosomes 

 undergo development in the sali- 

 vary glands of the fly and when 

 they reach the infective stage are 

 injected into the blood of other membrane 



human hosts by the bite of the fly. 

 The part of the cycle in the inverte- 

 brate host is thus radically different Wv ^^i^ J/uckus 

 from that of T. lewisi. In the BJepharoplast — ■■ 

 blood of an infected man the try- 

 panosomes are never present in Fig. 23. — Trypanosoma theileri 

 1 , mi r 1 (Bruce"), from blood of a cow. 



large numbers, ihey are lound {After Luhe). 

 in lymphatic glands and in the 



cerebrospinal fluid. Infection is accompanied in its early stages 

 by fever, enlargement of lymphatic glands and spleen, anaemia, 

 and wasting of the body. The lethargic condition which 

 generally precedes death, giving rise to the name "sleeping 

 sickness," accompanies the invasion of the central nervous 

 system by the trypanosomes. 



In addition to human sleeping sickness, Chagas' disease in 

 South America is due to a trypanosome. Many species attack 

 domestic animals, while others have been recorded from fishes. 

 Amphibia, reptiles, and birds. The genus Leishmania is likewise 

 important because of the human diseases Kala-azar and oriental 

 sore produced by some of its species. 



The spirochaetes represent a group of organisms of very great 

 importance and yet of highly problematical relationships. Some 

 investigators have thought that they are protozoans related to 



