STUDIES WITH ENDAMCEBA HISTOLYTICA 183 



portion of the pathogenic action of this parasite upon the tissues 

 of man and other animals was due to a toxin, or toxins, cytolytic 

 in nature, secreted by the organism, has been held for many years 

 by students of the subject, it was not until this demonstration that 

 it was shown experimentally that such agents did exist in the 

 parasite, and that alcoholic extracts contained these substances. 

 The work referred to demonstrated that in alcoholic extracts of 

 forty-eight-hour cultures of E. histolytica, grown upon the Locke- 

 Egg-Serum medium of Boeck and Drbohlav (1925), modified 

 by using human blood serum instead of horse serum, and in 

 Locke-Serum medium (Craig, 1926), there is present a hemolysin 

 capable of dissolving the red blood corpuscles of man, rabbits, and 

 guinea-pigs. This hemolysin was found to be thermolabile, being 

 destroyed when heated in a water bath at 60° C. and practically 

 insoluble in normal saline although soluble in absolute alcohol. 

 It was found not to be an exotoxin, as it could not be demon- 

 strated in the fluid portion of the cultures, in cultures in which 

 the amoebcC were dead, or in cultures over forty-eight hours old. 

 The experiments demonstrated that the hemolysin was intimately 

 connected with the living amoebae as extracts of cultures containing 

 only dead amoebae did not contain the hemolysin. 



These extracts of Endauuvba Jiistolytica also contained a cy- 

 tolysin capable of dissolving the epithelial cells of the mucous 

 membrance of the intestine of both man and cats, but neither 

 the hemolysin nor cytolysin was specific for the cells of man, as 

 already indicated, for the cytolysin dissolved the intestinal epi- 

 thelium of both man and cats, while the hemolysin dissolved the 

 red blood corpuscles of man, cats, and guinea-pigs. Bacteriolytic 

 substances could not be demonstrated in the extracts, and this 

 observation is significant in view of the well-known fact that 

 Endanuvha histolytica does not ingest bacteria under normal con- 

 ditions in man although it does ingest and dissolve the red blood 

 corpuscles of its host. 



The observations mentioned, although of much interest from the 

 standpoint of the etiology of the lesions characteristic of the in- 

 vasion of the tissues of man and experimental animals by End- 

 ama:ha Jiistolytica, are not of as great theoretical and practical 

 interest as the fact that these extracts, when used as antigens in 

 a complement fixation test, have been found capable of demon- 

 strating the presence of complement fixing bodies in the blood 



