STUDIES WITH ENDAMCEBA HISTOLYTICA 189 



of amoeba other than Endauurha histolytica was present, and from 

 these results it is evident that infestation of the intestine by species 

 of amoebae other than E. histolytica or by flagellates does not 

 cause a positive complement fixation reaction in blood sera with 

 the antigenic extracts used in this series of experiments. 



The individuals giving a negative complement fixation test 

 were mostly in hospital and were suffering from a wide range of 

 disease conditions, so that it is justifiable to state that disease 

 conditions other than amoebic infection, with the possible excep- 

 tion of rare cases of syphilis, as will be noted later, do not give a 

 positive reaction with this test. 



Relation to the Wassermann and Kahn Tests. As the antigenic 

 extracts used in the complement fixation test for infection with 

 E. histolytica were not prepared from pure cultures of the parasite, 

 as these are not yet available, and contained extractives not only 

 from the amoebae but also from the bacteria growing in the cultures 

 and from the culture medium, it was thought possible that the 

 positive results obtained might be caused by non-specific sub- 

 stances in the extracts, as is the case wnth the antigens used in 

 the Wassermann and Kahn tests for syphilis, in which non- 

 specific substances in the extracts of the tissues used are capable 

 of reacting with substances in the patient's blood serum and fixing 

 complement. In order to obviate this source of error, and to ascer- 

 tain whether the positive results obtained might be due to syphilis, 

 or not, a check of as many of the sera tested as possible was made 

 by ascertaining the result of the Wassermann and Kahn tests, as 

 well as the complement fixation test for amoebic infection, and it 

 was found that. eleven, or eighteen per cent, of the cases giving a 

 positive complement fixation reaction for E. hystolytica also gave 

 a positive W^assermann and Kahn reaction, while forty-nine, or 

 81.9, gave a negative Wassermann and Kahn reaction. On the 

 other hand, of 481 cases giving a negative complement fixation test 

 for E. histolytica, forty, or 8.3%, gave a positive Wassermann 

 reaction, and forty-three, or 8.9%, gave a positive Kahn reaction, 

 while 441, or 91.7%, gave a negative Wassermann reaction, and 

 438, or approximately ninety-one per cent, gave a negative Kahn 

 reaction. 



In interpreting these results it should be remembered that the 

 vast majority of the sera tested were obtained from our serological 

 laboratory and from patients whose blood sera had been submitted 



