IMMUNITY. THEORIES OF IMMUNITY 



the rule, and this forms the basis of Ehrlich's theory. If, after repair 

 has taken place, new quantities of toxin are administered at proper 

 intervals and in suitable quantities, the side-chains that have been pro- 

 duced by the regenerative process are taken up anew in combination 

 with the toxin, and so again the process of regeneration gives rise to the 

 formation of fresh side-chains. "The lasting and ever-increasing 

 regeneration must finally reach a stage at which such an excess of side- 



FIG. 39. THEORETIC FORMATION OF ANTITOXINS. 



The central white area represents a molecule of a cell; the shaded portion repre- 

 sents the cell itself; the surrounding area represents the body-fluids about the cell. 



r, A receptor of the molecule (first order) ; A, overproduction of receptors, which 

 are being cast oft'; A 2 , a cast-off receptor free in the body-fluids now an antitoxin; 

 A 3 , a molecule of antitoxin combination with a toxin molecule T 3 . A 3 , a cast-off 

 receptor still within the parent cell ; T, a toxin molecule hi combination with the re- 

 ceptor of a cell molecule; T 2 , a toxin molecule free in the body-fluids; T 3 , a toxin 

 molecule in combination with antitoxin; T 4 , a molecule of toxoid (toxophore group 

 lost). 



chains is produced that, to use a trivial expression, the side-chains are 

 present in too great a quantity for the cell to carry, and are, after the 

 manner of a secretion, handed over as a needless ballast to the blood. 

 Regarded in accordance with this conception, the antitoxins represent 

 nothing more than side-chains reproduced in excess during regeneration, 

 and therefore pushed off from the protoplasm and so coming to exist in the 

 free state" (Ehrlich). 



