SECTION II. 

 FERMENTS AND DIGESTIVE PROCESSES. 



CHAPTER VI. 



ENZYMES AND OTHER FERMENTS. DIGESTION. 



In the course of time the conception of fermentation has 

 undergone many changes. The notion was first associated 

 with those processes in which a bubbling or boiling condition 

 without application of heat was observed, and later, as the 

 most familiar kind of fermentation was more closely studied, 

 this phenomenon was found to be due to the escape of gas. 

 This escape of gas came finally to be recognized as the essen- 

 tial feature of fermentation and many operations bearing no 

 relation whatever to alcoholic fermentation were, through con- 

 fusion of ideas, frequently associated with it. 



The real fermentation, which follows when saccharine 

 juices are exposed to the air, had been studied in a way from 

 the remotest antiquity, but no rational attempts at an explana- 

 tion of the process were made until after the middle of the 

 seventeenth century, when the relation of alcohol and the gas 

 to the destruction of the sugar seems to have been fully recog- 

 nized. Several other reactions were associated with the alco- 

 holic fermentation; in the leavening of bread the production 

 of a gas was recognized, and it was noticed that in the changes 

 going on in the animal intestine gases were also liberated fol- 

 lowing the digestion of foods. Along with the alcoholic fer- 

 mentation there was included under the general name the pecu- 

 liar change which takes place when the wine formed from 

 saccharine liquids was allowed to stand exposed to the air. 

 To be sure no gas was formed in this action, as in the other, 

 but something in common was recognized. In both cases it 



