70 
PRINCIPLES OF BACTERIOLOGY 
chains takes place, several hundred will be formed in¬ 
stead of just six. The body cell does not need them; 
what becomes of them? Not being needed, they are 
cast off into the circulation and there combine with the 
poisons which originally were the cause of their forma¬ 
tion (Fig. 10). In order to understand the importance 
of this, let us take a concrete example: let us suppose 
Fig. 11.—Illustration of Ehrlich’s theory in case of diphtheria. 
A. A body cell (a) is injured by diphtheria toxin; (cd) through the union 
of the latter with the receptor (immune body on side chain, b ). 
B. As a result of this the toxin and the receptor (immune body or side 
chain) are thrown off. 
C. New receptors are formed to replace the one which had been thrown 
off, but, according to Weigert’s law of overproduction or overcompensation, 
instead of one receptor many more (three in the illustration) are produced. 
D. Only one receptor is needed to replace the lost ones, and the other 
two receptors are cast off. 
B. These two free receptors (immune bodies or side chains) having been 
produced as a result of stimulation by diphtheria toxin, have now a special 
affinity for it and will, whenever they meet it unite with it, thus protecting 
the body cell by intercepting the toxin ( cd ). 
