260 NATURE AND LIFE. 
the saliva a principle called ptyaline, which, like diastase, 
converts amylaceous matter into sugar. The gastric juice 
contains another principle, pepsin, which has the effect of 
liquefying albuminous substances, so that they may be pre- 
pared forabsorption. The pancreatic fluid contains another 
principle which acts in a similar way. Digestion is thus re- 
duced to a series of fermentations, as the ancient chemists 
had rightly conjectured in regard to it. These different 
phenomena, as well as those in which organisms take part, 
have the two general characteristics of fermentation; they 
occur only within certain limits of temperature, and the 
weight of the fermentable matter is always much greater 
than that of the ferment which suffices to decompose it. 
To conclude, fermentations occasioned in certain media, 
by the act of development and nutrition of ascertained 
microscopic animal or vegetable existences, present a group 
of well-defined characteristics. They follow obediently all 
the variations that may occur in the physiological activity 
-of the microscopic beings contained in the liquid. This 
does not go into fermentation all at once; it delays more 
or less, and molecular movement makes itself perceptible 
in it by degrees. The phenomenon is one of evolvement. 
This appears to be the characteristic of alcoholic, lactic, 
acetic, butyric, glyceric, and putrid fermentations—all of 
those, in short, which Pasteur has studied with so convin- 
cing accuracy. Is it the same with the conversion of amyla- 
ceous substances into sugar, under the influence of diastase 
or ptyaline, with the dissolving of proteic substances by 
pepsin, with the change of amygdaline into the essence of 
bitter-almonds, by contact with synaptase? Evidently 
not. These phenomena present another aspect; they show 
no stages of evolvement. Doubtless they require a certain 
time for their completion; but they take place all at once, 
and without any relation to the surrounding air. 
These differences between the two kinds of fermenta- 

