ENZYMES AND OTHER FERMENTS DIGESTION. I I/ 



of a substance produced in germinated barley; this substance 

 possessed the power of converting starch into a sugar which, 

 from its origin, was called malt sugar. Payen and Persoz, in 

 1833, succeeded in isolating the assumed ferment from the 

 sprouted barley, which they termed diastase. About the same 

 time it was recognized that saliva contains a similar starch- 

 converting agent which was later separated and called salivary 

 diastase or ptyalin. The seeds of the bitter almond were stud- 

 ied by several scientific men and Liebig and Wohler isolated 

 a ferment body which they termed emulsin. This has the 

 property of converting the glucoside called amygdalin into 

 glucose, prussic acid and oil of bitter almonds, or benzoic alde- 

 hyde. As the saliva was found to contain a ferment acting 

 qn starches, so the gastric juice was recognized as active 

 through the presence of an analogous body called pepsin which 

 acts on proteins. 



Most of these discoveries were made before 1840. The 

 ferments in the bitter almond, in sprouted barley, in the saliva 

 and in the gastric juice were all found to be soluble in water. 

 They were therefore called soluble ferments as distinguished 

 from the yeasts and the ferments of acetic, lactic and butyric 

 acids, and from the conditions of their action Liebig \vas led 

 to formulate the first general theory of fermentation, the mo- 

 lecular vibration theory. 



THEORIES OF FERMENTATION. \ 



Liebig's Theory. Liebig advanced and maintained for 

 years this view : A ferment is a chemicaf substance whose 

 particles or molecules exist in a peculiar state of vibration, and 

 in contact with other bodies this ferment is able to set up 

 similar states of vibration which result in the breaking down 

 of the bodies mixed with the ferment. Ferments were con- 

 sidered along with bodies undergoing putrefaction, and many 

 such substances were supposed to be able to bring about real 

 fermentations. According to a somewhat older view ferments 

 were said to act by their mere presence; that is they exerted 



