PARENTERAL DIGESTION AND IMMUNITY 251 



Rapidly following upon this came the discovery in France 

 and Germany by Bordet and Pfeiffer, respectively, that the 

 latter form of immunity demanded the presence of two orders 

 of substances in the body fluids of the immunized animal. How 

 great was the confusion is indicated by the fact that for one 

 of these, Pfeiffer's "immune body" and Bordet's "substance 

 sensibilatrice," the other names of " amboceptor," " fixateur," 

 " intermediate body," " sensitizer," " preparator," " desmon," 

 " copula," were proposed by various workers. Nor was the 

 confusion lessened by the continuing fight between the German 

 humoralists, who were satisfied to study the phenomena mani- 

 fested by the body fluids alone, and the Franco-Russian cellidar- 

 ists, led by Metchnikoff, who, with broader histological insight, 

 laid stress upon the cellular reactions to infection. 



The third phase was that of the ascendency of Ehrlich's 

 " side-chain theory " of immunity. It was found that antibodies 

 present in the blood serum neutralized the toxins ; all the in- 

 dications were that chemical interaction went on between the 

 two, but toxins were active in such extraordinary minute quanti- 

 ties, and also were produced in such minute quantities, that 

 chemical methods of analysis revealed nothing beyond the 

 probability that they were to be regarded as protein degradation 

 products. The biological test was far more delicate than the 

 chemical. We were, in fact, beyond the realms of chemical 

 technique. If confusion were not to be worse confounded, it 

 was necessary to have some working plan whereby to visualize 

 the processes that went on in the reaction between the micro- 

 organism and its products and the organism. This Ehrlich 

 afforded in his celebrated side-chain theory. Some may to-day 

 criticize that theory, and may gird at its toxins, toxoids, and 

 toxones, its haptophores of the first, second, and third orders, 

 its end-piece and mid-piece of the complement. But unquestion- 

 ably it afforded a working scheme, whereby a common basis 

 for expression of phenomena was afforded, and, equally un- 

 questionably, it promoted an enormous burst of activity in the 

 study of immunity problems. What is more, although Ehrlich 

 cautiously refrained from suggesting or premising any particular 

 element in the cell as being provided with side-chains, his theory 

 was based upon the only rational conception of cell metabolism — 

 that which regards the molecule of living matter as of extra- 



