GENERAL BACTERIOLOGY 
71 
that a body cell was injured by diphtheria exotoxin; 
let us further suppose that four side chains combined 
with this exotoxin; the body cell is injured but re¬ 
covers; these four side chains combined with the exo¬ 
toxin are cast off; new side chains are formed—not 
four but many more, according to Weigert’s law; four 
of these new side chains are retained by the body cell 
to replace the old ones, the rest are thrown off into 
the circulation; having been formed as a result of in¬ 
jury to the cell by diphtheria exotoxin, these free sid^ 
chains, circulating in the blood, have the same affinity 
for the diphtheria exotoxin as if they were attached 
to the body cell, and because of this affinity, wherever 
they will meet the diphtheria exotoxin, they will com¬ 
bine with it, and, in this way, protect the body cell; 
because if it were not for their combining with the 
exotoxin, the latter would reach the body cell and 
would there combine with it by means of the side chains 
which remained there (to replace the four original 
side chains), and would do the same damage to the 
cell as it had done before (Fig. 11). 
It is quite clear, therefore, that these free side chains 
are the antitoxins—they neutralize or combine with the 
exotoxins. This explains how a patient recovers from 
diphtheria; it explains why he remains immune (for 
some time or forever) after one attack of the disease; 
and, finally, it explains why such blood if injected into 
another animal would protect the latter from such in¬ 
fection. After the horse has been several times in¬ 
jected with the diphtheria exotoxin, his blood'is full of 
these antitoxins (the side chains) and when injected 
into the patient, these side chains combine with the 
exotoxins in the patient’s blood and thus protect him, 
in not allowing the exotoxins to reach the body cells 
and injure them. If a certain individual has no cor- 
