THE RELATION OF LIPOIDS TO IMMUNITY 523 



Later Weichardt made the reaction more accessible to practical use 

 by introducing into the solution of serums and antigen a system composed 

 of sulphuric acid and barium hydroxid, together with certain catalytic 

 agents. Using phenolphthalein as an indicator, he could show that 

 fresh serums in high dilutions alter the surface tension of the finely 

 divided barium sulphate particles by their colloidal action, so as to in- 

 crease the absorption of H-ions, thus rendering the solution more alkaline. 



This phenomenon has been utilized by Weichardt, under the name 

 of "epiphanin reaction," to determine the occurrence of such interac- 

 tion of antigen and antibody. The reaction probably depends upon 

 physicochemical principles of absorption, but the exact nature of the 

 change is not yet understood. The reaction is based upon the following 

 generalizations : 



1. Solutions containing colloids i. e., antigen alone, antiserum alone, 

 or antigen plus non-specific antiserum in certain dilutions act in the 

 foregoing system by shifting the phenolphthalein end-point (the point of 

 neutralization when acid and alkali are brought together in the presence 

 of this indicator) in the sense of increased OH-ions (pink color). 



2. Specific antigens can inhibit the activity of their specific antise- 

 rums, the specific antigen-antibody combination then becoming evident 

 in vitro by a shift of the end-point in the sense of increased H-ion con- 

 centration (light color). 



Specificity. The specificity of the reaction has been confirmed by a 

 number of investigators who used the test for the identification of a 

 host of antigen-antibody combinations in vitro. The underlying prin- 

 ciples have been confirmed by Kraus and Amiradzibi, 1 Schroen, 2 

 Seifert, 3 Mosbacher, 4 and others. The reaction has been applied to a 

 study of various antigens and their antibodies, such as diphtheria toxin, 

 tetanus toxin, typhoid and tubercle bacilli, tumor extracts and placenta 

 extracts by Weichardt; extracts of syphilitic livers and serums of 

 syphilitic patients by Seifert, Keidel and Hurwitz. 5 



Technic. The technic of this reaction has been modified from time 

 to time. The method here given is essentially the latest given by 

 Weichardt, 6 slightly modified by Keidel and Hurwitz. 



1 Zeitschr. f. Immunitatsforsch., 1910, vi, 16. 



2 Munch, med. Wochenschr., 1910, 38, 1981. 



3 Deutsch. med. Wochenschr., 1910, 50, 2333. 



4 Deutsch. med. Wochenschr., 1911, 22, 1021. 

 6 Jour. Amer. Med. Assoc., 1912, lix, 1257. 



6 Berl. klin. Wochenschr., 1911, 43, 1935. 



