192 RESEARCH IN PROTOZOOLOGY 



of rabbit kidney and pig- serum, will develop an antibody to their 

 own tissue lipoids. 



It is probable that the substance, or substances, in the alcoholic 

 extracts of E. histolytica used in this series of experiments, are 

 similar to the bodies in the alcoholic extracts mentioned above 

 and it will be possible, when pure cultures of this parasite are 

 obtained, to determine whether specific antibodies are formed in 

 the blood of man in response to injections of alcoholic extracts of 

 such cultures. 



The practical value of the complement fixation test in the diag- 

 nosis of infections with E. histolytica is still undetermined, and is 

 greatly limited by the difficulty of making the antigenic extracts 

 and the small amounts obtainable. The cultivation of E. histolytica, 

 while not difficult in trained hands, is not easily accomplished, by 

 the average laboratory technician, and the maintenance of such 

 cultures for weeks and months, as is necessary in order to keep 

 such antigenic extracts on hand, is a matter of considerable tech- 

 nical difficulty. In addition, not every extract made from the 

 cultures is antigenic, for we have several times obtained inert 

 extracts from the same strain of £. histolytica that had given and 

 afterwards gave excellent antigenic extracts, although the inert 

 and active extracts were prepared in the same manner. 



Clinically, and as checked by the results of feces examinations, 

 the test would appear to possess a high degree of specificity, and 

 in its use in hospital practice here has repeatedly proven its 

 value in demonstrating amoebic infections that would otherwise 

 have remained unrecognized. The test does not give a positive 

 reaction in other diseases or infections, except in rare cases of 

 syphilis, as proven by the fact that such reactions have not been 

 encountered in the hundreds of cases of miscellaneous diseases 

 and infections that have been tested during the progress of these 

 experiments, so that it may be stated that it is a very highly 

 specific test when positive, and almost as specific in demonstrating 

 the absence of /:. histolytica, when negative. However, our experi- 

 ence has been that practically all individuals giving a positive re- 

 action with the test have also showed E. histolytica in the feces, so 

 that the diagnosis of the infection could have been made by a 

 fecal examination. In many patients, however, such an examina- 

 tion would not have been requested, owing to the absence of, or 

 mild character of the symptoms of amoebic infection present, or 



