MOLECULAR COMPLEMENT ARINESS IN ANTIGEN- ANTIBODY SYSTEMS 15 



Fig. 7. Apparent distance of approach of trimethylammonium group of hapten 

 to carboxylate of antibody. 



TABLE 6 

 Effect of ion radius in 



N(CH3)3+ system 



of pyridinecarboxylate ions. From the extent of combination of nicotinate, 

 750-nicotinate and picolinate ion with antibodies prepared against the azoben- 

 zoate ions, it appears that the position occupied by the nitrogen atom in the 

 ring acts as though it were a carbon of a benzene ring connected to a large 

 steric substituent. The nitrogen atom, instead of acting smaller than the CH 



