• A Theory of Ferments and Their Action. 
39 
been slightly sensitized to horse serum by , the administration, subcuta- 
neously and by feeding methods, of large quantities of the sera of ani- 
mals other than the horse, but this result does not disprove the state- 
ment, that sensitizing a guinea pig to horse serum is quantitivelv a 
specific reaction. But the sensitizing reaction is not limited to horse 
serum and guinea pigs, since it has been accurately duplicated when 
other sera have been introduced into alien animals. Aside from the 
sensitizing feature of the process, the reaction that follows the intro- 
duction of a serum into an alien animal differs apparently in no respect 
from that already mentioned which follows the introduction of a fer- 
ment, toxin, or proteid into the blood of a non-immune animal; and 
further than this, the relations that exist between the serum of the 
horse and that of the pig, indicated by the term “alien,” and between 
a pathogen and the blood serum of man, indicated by the term “non- 
immune,” relations which are necessary to the reactions that occur, 
affords evidence, seemingly conclusive, that the reactions in these pro- 
cesses is that which take place between a ferment and its substrate. 
The great importance of these facts, which have been revealed to us by 
recent experimental work in biology of the blood, their present value 
to man, and, I am confident, the far greater future value that a clearer 
insight into their nature will disclose, will reveal many of the hidden 
mysteries of life — among others those of proteid synthesis, immunity 
and metabolism. When the day arrives in which all these things shall 
come to pass the mind of man will be impressed, more than it is now, 
with the sublime truth of the Divine saying “The blood thereof is the 
life thereof.” 
