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 for absorption. 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- 



