190 RESEARCH IN PROTOZOOLOGY 



for a Wassermann and Kahn test, many of them from the venereal 

 wards of the hospital. Thus, it is nut surprising that the per- 

 centage of positive Wassermann and Kahn reactions is compara- 

 tively high in both the cases giving a positive and a negative 

 complement fixation test for amoebic infection. However it is 

 true that the percentage of positive results with the Wassermann 

 and Kahn tests in the cases giving a positive complement fixation 

 reaction for R. Jiisfolytica has been approximately ten per cent 

 higher than in the cases giving a negative complement fixation 

 test for E. histolytica. It is also significant that of the eleven cases 

 giving a positive reaction with all three tests, no less than six 

 did not show E. histolytica in the feces. In view of these findings 

 it is probable that, in rare instances, cases giving a positive reaction 

 with the Wassermann and Kahn tests will also give a positive 

 reaction with the complement fixation test for E. histolytica, and in 

 patients who give such a reaction, and in whom the parasite cannot 

 be demonstrated, the positive result should not be considered as 

 diagnostic. However, repeated microscopic and cultural examina- 

 tions of the feces should be made for E. histolytica before con- 

 sidering the positive reaction as a false reaction. 



While such cross-complement fixation apparently occurs, in 

 rare instances, with this test, it is not surprising because of the 

 crude nature of the antigenic extracts that are used, and it will 

 not be until extracts can be prepared from pure cultures of E. 

 histolytica, that this source of error will probably be obviated. 

 Admitting that such false reactions may rarely occur, it is evident 

 from the results of this series of experiments that, in the vast 

 majority of cases, the complement fixation reactions obtained with 

 the antigens employed were specific in nature and were not caused 

 by non-specific substances in the antigenic extracts analogous to 

 those producing the positive complement fixation reactions with the 

 antigens employed in the Wassermann and Kahn tests. 



Discussion of Results. The results of the experiments detailed 

 in this contribution demonstrate that specific antibodies are pro- 

 duced in the blood serum of man in infections with E. histolytica 

 and it is significant that the patients giving the strongest com- 

 plement fixation reactions were those showing the mildest symp- 

 toms of the infection, or no demonstrable symptoms, while those 

 having severe dysentery gave weaker reactions, thus indicating 

 that complement fixation is an index to the resistance of the in- 



