1893, ON PASTEUR’S METHOD OF INOCULATION. 107 
fermentation by the unmodified ferment. In the same way, it ought 
to be possible to modify the microbe of putrefaction so as to produce 
a decay-proof body. 
With regard, again, to the other explanation that the modified 
microbe confers immunity by the secretion of some toxic principle 
which prevents the growth of the unmodified form, it might be asked : 
(1.) Would not the secretion—or production in any way—of 
such a toxic principle be highly injurious to the animal in which it 
was secreted ? 
(2.) Why should a toxic principle be allowed to remain in the 
system for the year required by Pasteur’s view on inoculation for 
splenic fever, or for the seven years required by the received view on 
vaccination ? 
(3.) Would not the mere existence in the blood and tissues of the 
number of microbes necessary to produce a sufficiency of the toxic 
principle be in itself enough to produce the unmodified disease ? 
Dr. Klein (‘‘Micro-organisms and Disease”) adopts this 
‘* Antidote theory ” of inoculation. 
But apart from the difficu!ties I have hinted at above, another 
arises for Dr. Klein, in the fact that he himself adopts the view that 
death, in the case of any disease caused by a microbe, is due to the 
chemical alteration produced in the blood and tissues. That is tosay, 
either a change is produced in the blood analogous to that from 
sugar to alcohol effected by the yeast-plant, or a special ferment is 
secreted by the microbe. Thus the same toxic principle which causes 
death in the disease, is the cause of immunity from the disease 
when the animal is inoculated. 
Now if we suppose the microbe used for inoculating increases as 
much as the unmodified form, then it ought to produce as great an 
amount of the toxic principle, and hence cause the disease in as 
severe a form. If, on the other hand, by increasing less, it produces 
less of the poison, we cannot suppose there would be sufficient to 
prevent the growth of the unmodified microbe if introduced; for it 
is to be remembered that the unmodified microbe is supposed to go 
on increasing until it has produced sufficient of the poison to prevent 
its own further growth. This is the explanation of the cessation of 
the disease. Hence the amount of poison necessary to prevent the 
growth of the unmodified microbe—in other words, to prevent the 
disease—is the same as that required to produce the normal type of 
the same. No amount of the toxic principle less than what would 
itself produce the disease, can be sufficient to prevent the growth of 
the unmodified microbe—that is, to prevent the disease. 
Thus, then, as it appears to me, neither the ‘ Exhaustion 
theory” nor the ‘‘ Antidote theory” explains immunity from disease 
conferred by inoculation. 
An assumption which underlies both explanations is, that 
after a certain number of generations, the microbes are obtained 
