SUMMARY AND DISCUSSION 187 



plementariness in structure as the basis of the specificity of interaction of anti- 

 bodies and antigens. This idea represents a refinement of Ehrlich's lock-and- 

 key concept. The idea is that weak intermolecular forces, which individually 

 would not be enough to produce a significant bond, may cooperate between 

 molecules that are complementary in structure in such a way as to produce a 

 strong bond. 



It is my opinion that the conclusions that have been reached through the 

 studies of serological systems are completely reliable, that there is no doubt that 

 the specificity of antibodies results from their having a structure complementary 

 to that of the antigen, and that the forces that operate between molecules of 

 antigen and molecules of antibody are weak intermolecular forces that individ- 

 ually are non-specific, but that become specific because of the spatial relation- 

 ship of the different parts of the combining region of the antibody in relation 

 to the surface structure of the antigen. 



So far as I am aware there is only one alternative idea about specificity: that 

 there is a special sort of interaction between identical molecules. According to 

 this idea a gene can direct the manufacture of another gene because there is an 

 interaction between two identical molecules that is different from that between 

 one molecule and another molecule that is not identical with it. Professor Jehle 

 talked about a theory of this sort. I must say that I am skeptical about the 

 significance of Professor Jehle's theory. I do not doubt the correctness of his 

 equations, but I think that the special terms in the expression for the energy 

 of interaction of identical molecules have values so small in comparison with 

 kT, the energy of thermal agitation, as to permit them to be ignored. 



Professor Haurowitz raised the question of whether antibodies can be manu- 

 factured after the antigen is gone. The speakers here have, I think, agreed that 

 it is likely that an antigen must be present in order to have continued production 

 of antibodies. We were, perhaps, unfortunate at this symposium in not having 

 somebody present to support the other point of view. 



Dr. Pressman in his talk mentioned some of the evidence that shows that the 

 antibody molecule fits tightly around the haptenic group of an antigen, the fit 



o 



being better than an atomic diameter — within about an Angstrom, whereas 

 atoms are about 4 Angstroms in diameter. Serious steric hindrance occurs if a 

 methyl group is introduced in the hapten in place of a hydrogen atom, increas- 

 ing the radius by less than 1 A. Introduction of a chlorine atom, a bromine 

 atom, or an iodine atom produces larger steric hindrances. 



Dr. Pressman also mentioned the experiments that show that there is an 

 electric charge of opposite sign to that in the haptenic group of the antigen 

 within a couple of Angstroms of the minimum distance of approach. The ratio 

 of combining powers of the charged and uncharged haptens was found to be 

 about 15, which corresponds to about a 7 A distance. 



Dr. Wilson mentioned that in the measurements that he has made of the 



