THE CHEMISTRY OF DIGESTION 987 



of the tissues to utilize them. For this reason, the disaccharides, such 

 as cane-sugar, maltose, and lactose, are first converted into mono- 

 saccharides, such as dextrose, levulose, and galactose, while the pro- 

 tein molecule is split up into amino-acids. 



Ferments. — The word ferment was formerly applied to living 

 organisms such as the yeast cells, which during their conversion 

 of sugar into carbonic acid and alcohol, cause the liquid to boil up 

 (f ervere), owing to the evolution of this gas. For similar reasons this 

 entire process was designated as fermentation. In recent years, 

 however, many similar substances have been found in animal and vege- 

 table cells, so that the term of ferment is now applied to all those com- 

 plex organic bodies which are capable of inciting a chemical reaction 

 without they themselves undergoing a quantitative or qualitative alter- 

 ation. Hence, any fermentation must derive the energy evolved in 

 the course of this process from the substances concerned in it and not 

 from the activating agent. Besides, no direct relationship can exist 

 between the amount of the ferment and the intensity of the reaction. 

 This imphes that even the most minute amounts of ferment are capable 

 of inducting chemical changes in proportionately much larger quan- 

 tities of reducible material, and that the addition of more ferment can 

 only serve to quicken the reaction, and not to alter its character. A 

 chemical change of this kind is known as a catalysis, while the agent 

 producing it is designated as a catalyzer or catalyst. The sub- 

 stance acted upon by the catalyzer is termed the substrate. There 

 are, of course, many other catalytic agents besides the ferments. 

 Thus, potassium chromate may act as the catalyzer for the oxidation 

 of hydriodic acid by bromic acid or spongy platinum, and may cause 

 the spontaneous combustion of hydrogen peroxide into water and 

 oxygen. 



Until comparatively recently, ferments have been classified as 

 organized and unorganized, or as hving and dead. Among the former 

 might be mentioned the yeast plant or saccharomycetes, and a large 

 number of bacteria, and among the latter, the different active princi- 

 ples of the digestive juices, such as ptyalin, pepsin, trypsin, and others. 

 On the one hand, therefore, we have living cells possessing a distinct 

 organization, and, on the other, dead sustances, which in most 

 instances have not been satisfactorily isolated and are known to be 

 present solely from the reactions incited by them. While this classifica- 

 tion is easily understood, it is no longer tenable, because it has been 

 shown that the yeast cell and allied hving entities may be made to 

 give up their ferments by chemical means without that the latter 

 lose their power of inciting fermentation. In other words, it is not at 

 all essential to the action of the ferment that it be carried by hving 

 matter, and hence, it must be considered merely as a product of cellular 

 metabolism. Consequently, it is really as '^ unorganized" as the 

 enzyme of the cells of the salivary glands or any other (Buchner 

 1897), and hence, the terms of ferment and enzyme are now synonymous 



