TEYPANOSOMA CKUZI 667 



of tlie parasites followed administration of these bodies, but 

 their application to natural infections has not as yet met with 

 decided success. Sufficient, however, is known to justify further 

 investigations of a similar kind. It has been observed that a 

 tolerance of such reagents can be developed by the trypanosomes, 

 and this fact may complicate the problem at issue. 



Both normal serum and the serum of infected animals have 

 been found to possess trypanocidal and protective properties, 

 and in certain cases a degree of immunity has been established 

 as the result of light infections. It has not hitherto been 

 possible, however, to produce such a degree of immunity as 

 could be utilised either for prophylactic or therapeutic purposes. 

 The serum of an infected animal may manifest a specific 

 agglutination reaction towards the infecting trypanosome. 



Other Pathogenic Trypanosomes. — Apart from sleeping sick- 

 ness no other important disease of man has been found to be 

 associated with trypanosomal infection, but some observations 

 on a condition observed in Brazil may be alluded to. 



Trypanosoma cruzi. — Chagas, working in Brazil, observed this 

 trypanosome in a monkey, the intermediate host being hemipterous insects 

 of the genus Cmwrhinus. As these insects also feed on man, the pos- 

 sible relationship of the trypanosome to a human disease occurring in 

 that region was considered. This disease affects children, and gives rise 

 to pronounced amemia, the occurrence of oedema, and enlargement of 

 lymphatic glands, the spleen, and liver; it may cause death in a few- 

 weeks, or assume a chrouic form lasting for years and characterised by 

 disorders of internal secretion (myxoedema, bronzing of skin) and 

 infantilism. The trypanosome is not found in large numbers in the 

 peripheral circulation in such cases, but when the blood is injected into 

 guinea-pigs, or into callithrix monkeys, a definite disease occurs, leading 

 to death. The special feature of interest is the development of the 

 parasite occurring in the lungs of gninea-pigs. Here within the endo- 

 thelial cells the organisms assume a round or pyriform shape with one 

 nucleus which divides to form eight bodies resembling somewhat the 

 merozoite form of the malarial parasite. It is supposed that these escape 

 and infect the red blood cells, as in the circulating blood erythrocytes 

 containing merozoite bodies are present, and from these a trypanosome 

 develops within the red cell. Post mortem in man, the parasite occurs 

 chiefly in the cardiac and voluntary muscles and in the central nervous 

 system, in which situations the tissue cells may contain enormous numbers 

 of the organism in a small round or pear-shaped form with tropho- and 

 kineto-nuclei but no flagellum or undulating membrane. A cycle of 

 development also takes place in the intestinal tube of the conorhinus, and 

 cultures are obtainable on Novy and MacNeal's medium. There is little 

 doubt that the trypanosome is the cause of the disease. 



It is beyond the scope of this work to deal at length with the 

 other diseases of animals caused by trypanosomes. The chief of 

 these have been mentioned in the opening paragraph, but it may 



