90 ADAPTATION AND DISEASE 



(v.) The Mechanism of Immunity. — One more postulate 

 needs to be laid down. You will remember how I pointed out 

 in my second lecture that the introduction of toxines, whether 

 phytotoxins like abrin, or bacterial toxins like those of diphtheria 

 and tetanus, lead to the abundant if not over-production of 

 antitoxins on the part of the cells. 



The simplest explanation of this continued production is 

 that when the toxin (which has all the earmarks x of an enzyme) 

 enters the cell, it combines with and detaches certain side-chains. 

 Whether the cell in consequence becomes destroyed or, on the 

 other hand, succeeds in neutralizing the toxin, depends upon 

 two factors — the number of toxin molecules that gain entrance, 

 and the rate at which the cell can reproduce the lost side-chains. 

 Just as a damaged crystal if placed in a saturated solution of 

 the particular salt repairs itself, so we have to assume the capacity 

 on the part of the living molecules to build up lost parts. So 

 long, that is, as the toxin in the cytoplasm acts as a catalyst 

 detaching the particular side-chains, for so long will the molecular 

 complexes build up side-chains until from the law of habit this 

 building up exceeds the immediate need of the cell, and the 

 side-chains being in excess are excreted to become the antitoxins 

 of the blood serum. We must, that is, regard these side-chains 

 as now built up in series from the simpler cytoplasmic molecules 



of the cell-sap, and when 



V 



3***^ 



FlO. 11. 



so built up easily liberated. 

 Here parenthetically it de- 

 serves note that the bodies 

 which are antitoxins for man 

 are toxins for the bacteria 

 — all, in fact, depends upon 

 the point of view. 



That this conception of 

 the mechanism of immunity and progressive adaptation 2 is 

 substantially correct has, I urge, been shown by the later 

 admirable studies of Professor Victor C. Vaughan of Ann 

 Arbor, Michigan, and Abderhalden of Berlin. Vaughan was 



1 Corrected from " properties " in the lecture as delivered, this being the 

 more accurate statement. 



2 A conception laid down by me in 1908 in my Principles of Pathology, 

 though there following naturally upon my article upon " Inheritance " published 

 in 1901. 



