138 IMMUNO-CATALYSIS 



after the injection and persisted there during a period of ten days. 

 However, the same amounts of antibodies injected after being fixed 

 by the antigen do not appear in the serum. 



It is evident from the above results that the combining groups of an 

 antigen, when free, are able to produce in vivo antibodies with specific 

 combining groups. When the combining or antigenic groups of a mole- 

 cule are saturated with antibody and kept saturated in vivo with excess 

 antibody they are unable to incite the formation of antibodies. Ap- 

 parently the antigen -f- antibody ;=^ antigen-antibody complex equilib- 

 rium is completely shifted to the right in the presence of an excess 

 amount of antibody. 



The question may therefore be asked whether the reverse process 

 does or does not take place. Namely, if the combining groups of an 

 antibody are saturated with antigen the former may fail to incite the 

 production of specific anti-antibodies, or antibodies to the specific 

 configuration or combining groups of antibodies involved in the anti- 

 gen-antibody reaction. The saturation of the combining groups of anti- 

 bodies would not block the species specific antigenicity of the antibody 

 globulins which would account for the formation of antibodies (when 

 combined with antigen) which are reactive with normal globulins from 

 the same species. In view of the above consideration one may question 

 the validity of the conclusions drawn concerning the absence of anti- 

 antibody formation in experiments involving the use of the above 

 mentioned antigen-antibody complexes (Ando and associates, 1937, 

 1938; Treffers and Heidelberger, 1941) where combining groups of 

 both reactants are mutually saturated, and therefore are incapable to 

 negotiate the reactions required for the formation of anti-antibodies. 



g. Acquisition of New Antigenic Specificity by Antitoxins. The 

 question of whether or not antibody has acquired a new specificity 

 antigenically distinct from the corresponding normal globulins has been 

 investigated by various workers. Weil, Parfentjev and Bowman (1938) 

 made the following observations: (a) antibody response in rabbits, im- 

 munized with pepsin-treated antitoxin, is slight and delayed; (b) 

 tests for cutaneous hypersensitivity, and precipitin and complement 

 fixation tests all showed that the treatment with pepsin had eliminated 

 the original antigenicity of the antitoxin; and (c) guinea pigs sensitized 

 to pepsin-treated antitoxin were shocked by normal horse serum, but 

 not by the homologous antigen. The failure to shock the guinea pig 



