E. histolytica: immunological reactions 



gions although the incidence of infection is apparently 

 not much greater in the former. The consensus of opin- 

 ion seems to be that the resistance of the host is so 

 greatly lowered in the tropics that the amoebae are able 

 to invade the tissues sufficiently to bring about symptoms. 

 Other possible explanations are increases in the aggres- 

 sivity of the parasites due to rapid passage through the 

 hosts (see p. 105), the presence of more aggressive 

 strains in the tropics, mass infections due to favorable 

 w^eather and insanitary conditions, and the character of 

 the diet. 



8. immunological reactions 



Complement fixation. Very little attention has been 

 directed toward the study of immunity reactions in amoe- 

 bic infections and the data on this subject are therefore 

 few and indefinite. Izar (1914a) claims to have obtained 

 positive complement fixation, using aqueous antigens 

 from liver abscess pus and from the feces of infected 

 cats. Successful results were secured with the serum from 

 three cats and five persons infected with E. histolytica. 

 Hage (1920) was unable to confirm Izar's work. He 

 used antigens from liver abscess pus and from the feces 

 of infected human beings. He accounts for his failure on 

 the ground that any antigen present is too small in 

 amount to be extracted easily. Now that methods of cul- 

 tivating E. histolytica have been devised, a new source 

 of antigens is available. 



Precipitin tests. Wagener (1924) prepared antigen 

 from scrapings of ulcerated areas in infected cats and 

 obtained a positive precipitin test in cats infected for 



103 



