STUDIES WITH EXDAMCEBA HISTOLYTICA 191 



dividual or the severity of his reaction to the parasite. It is also 

 interesting to note that the positive complement fixation reac- 

 tion disappears promptly after appropriate treatment and the dis- 

 appearance of the parasite, thus demonstrating that if this is an 

 immune reaction, it disappears very soon after the disappearance 

 of the infection. In viev^ of the fact that there is no evidence of 

 immunity to infection with E. histolytica, as shown by the fact 

 that reinfections are very common, it is evident that complement 

 fixation in this infection cannot be considered as an index of 

 immunity but that it is rather an evidence of the presence of 

 living amoebcC in the tissues of the host. 



The exact nature of the bodies producing complement fixation 

 in this infection is unknown at present, but it is evident that the 

 substances present in the antigenic extracts which are used, are 

 similar in their nature to those present in other alcoholic antigenic 

 extracts, which depend, so far as known, upon specific lipoids in 

 the extracts which react with specific lipotropic substances in 

 the blood serum of the infected individual. These substances, 

 which are all characterized by the fact that they can be extracted 

 with alcohol, are of much interest and have attracted a great 

 deal of attention in recent years. As long ago as 191 5, I demon- 

 strated that alcoholic extracts of cultures of Mycobactcriiim tuber- 

 culosis fixed complement when used as antigens with the blood 

 serum of tubercular individuals, and this observation has since 

 been confirmed by Dienes and Schefif (1926), Lewis (1927), 

 and Furth and Aronson (1927), who have demonstrated that there 

 is a distinct substance in this bacterium, extractable with alcohol, 

 which fixes complement when used as an antigen with the blood 

 serum of tubercular patients. Similar alcohol-soluble substances 

 have been demonstrated in Coryncbactcriuin diphtheria; and Strep- 

 tothrix by Freud (1927) ; in Treponema pallidum by Craig and 

 Nichols (1912) ; in the cercaria of Bilharzia by Fairley (1927) ; 

 and in extracts of the intestine of rabbits filled with the tro- 

 phozoites of coccidia by Chapman (1929). 



In this connection the recent work of Kurt Meyer and of 

 Sachs, Klopstock, and Wile, is of interest. Kurt Meyer has shown 

 that antisera obtained by injecting rabbits with watery extracts of 

 tapeworms will fix complement in the presence of alcoholic ex- 

 tracts of the worms, while Sachs, Klopstock and \\\\t have 

 demonstrated that rabbits, when injected with alcoholic extracts 



