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 : 



(i.) 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 difficulties 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 to say, 

 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 



