124 THE SIDE-CHAIN THEORY 



could hardly expect to throw out of action all the agglutinable groups 

 in a given quantity of bacteria by treating these with a corresponding 

 agglutinin, even in very large amount. But notwithstanding this 

 difficulty Neisser and Lubowski obtained some sera by immunizing 

 with such mixtures, which contained no agglutinins at all. This, to 

 be sure, was exceptional; but they could show, nevertheless, that in 

 a series of experiments the subsequent agglutinative value averaged 

 only 1 to 106 as compared with 1 to 1093 in the control animals, 

 viz., in those which had been injected with non-agglutinated 

 organisms. 



On the basis of Ehrlich's theory the appearance of the so-called 

 natural antibodies in the serum can now also be accounted for in 

 a ready manner. Since the antibodies are not formed de now, but 

 merely represent normal molecular complexes of the body cells, it 

 can hardly be surprising that once in a while, even in the course of 

 normal events, some of these side chains will be cast off, although no 

 bacteria or their toxins may have entered the body. That the anti- 

 bodies, moreover, which result on immunization with foreign cells 

 or cell products should be specific, is a necessary consequence, if we 

 accept the view that antibody production presupposes the existence 

 of a special affinity between the haptophoric groups of antigen and 

 antibody. The remarkable point in this connection indeed is not so 

 much the fact that the injection of a toxin should give rise to an 

 antitoxin, or of bacteria to corresponding lysins or cytotoxins, but 

 that so many varieties of antibodies should be possible for a given 

 animal. 



On the basis of Ehrlich's theory we are forced to conclude that 

 the cells of the body collectively must contain at least as many 

 different types of side chains preformed as the number of different 

 antibodies that can be theoretically obtained from a given animal, 

 and vice versa. This, however, does not seem altogether likely, if 

 we bear in mind the innumerable varieties of antibodies that can 

 actually be produced. I would only recall the possibility of obtain- 

 ing specific precipitins to the albumins of almost all the different 

 types of animals, then again the production of agglutin ns not only 

 to different species of bacteria, but even to different strains of a 

 single species, etc. But it seems to me that even though we accept 

 Ehrlich's theory in its essential points that we need not suppose 

 the existence of such an enormous variety of receptors as occurring 



