AND THE CAUSES OF FERMENTATION. 117 
menters, in this line of research, cease to be the 
inexplicable puzzle which they must always appear to 
those who place implicit faith in the narrower and too, 
exclusive ‘vital’ theory of fermentation advocated. 
by M. Pasteur and his followers. 
My investigations have convinced me that, with 
regard to degree of fermentability, the various fer- 
mentable fluids and mixtures are divisible into three 
distinct subclasses :— 
I. There are what may be called self-fermentable 
* fluids or mixtures—that is, fluids or mixtures which, 
after exposure to a temperature of 212°F. or higher, 
are still capable of undergoing fermentative changes 
without the addition of less-heated matter, either not- 
living or living. The changes occurring in these self- 
fermentable fluids (in which pre-existing living things 
have been killed), when strictly protected from contact 
with adventitious particles, vary in rapidity and 
in intensity from the highest to the very lowest 
degrees of fermentability. These gradations are de- 
pendent principally upon the nature of the fluids or 
mixtures employed, and upon the degree of heat to 
which they have been submitted, though partly also 
to the temperature, pressure, presence or absence of 
filtered air, and degree of light to which the mixtures 
are subsequently exposed. For the sake of conveni- 
ence, these gradations may be ranged into several 
