COMPOSITION OF FOOD AND ACTION OF ENZYMES. 737 



ENZYMES AND THEIR ACTION.t 

 Historical. — The significance and use of the term fermen- 

 tation have varied greatly during the course of years. The 

 word at first was applied to certain obvious and apparently spon- 

 taneous changes in organic materials which are accompanied by the 

 liberation of bubbles of gas: such, for instance, as the alcohoUc 

 fermentations, in which alcohol is formed from sugar; the acid fer- 

 mentations, as in the souring of milk; and the putrefactive fer- 

 mentations, by means of which animal substances are disintegrated, 

 with the production of offensive odors. These mysterious phenom- 

 ena excited naturally the interest of investigators, and with the 

 development of chemical knowledge numerous other processes were 

 discovered which resemble the typical fermentations in that they 

 seem to be due to specific agents whose mode of action differs from 

 the usual chemical reactions, especially in the fact that the causa- 

 tive agent itself, or the ferment as it is called, is not destroyed or 

 used up in the reaction. Thus it was discovered that germinating 

 barley grains contain a something which can be extracted by water 

 and which can convert starch into sugar (Kirchhoff, 1814). Later 

 this substance was separated by precipitation with alcohol and was 

 given the name of diastase (Payen and Persoz, 1833). Schwann 

 in 1836 demonstrated the existence of a ferment (pepsin) in gastric 

 juice capable of acting upon albuminous substances, and a number 

 of similar bodies were soon discovered: trypsin in the pancreatic 

 juice, amygdalin, invertin, ptyalin, etc. These substances were all 

 designated as ferments, and their action was compared to that of 

 the alcoholic fermentation with yeast, the process of putrefaction, 

 etc. Naturally very many theories have been proposed regarding 

 the cause of the processes of fermentation. For the historical devel- 

 opment and interrelation of these theories references must be made 

 to special works.* It is sufficient here to say that the brilliant work 

 of Pasteur established the fact that the fermentations in the old 

 sense — alcoholic, acid, and putrefactive — are due to the presence 

 and activity of living organisms. He showed, moreover, that 

 many diseases are likewise due to the activity of minute living 

 organisms, and thus justified the view held by some of the older 

 physicians that there is a close similarity in the processes of fer- 

 mentation and disease. The clear demonstration of the importance 

 of living organisms in some fermentations and the equally clear 

 proof of the existence of another group of ferment actions in which 

 living material is not directly concerned led to a classification wliich 

 is used even at the present day. This classification divided fer- 

 ments into two great groups : the living or organized ferments, such 

 as the yeast cell, bacteria, etc.; and the non-living or unorganized 



* Consult Oppenheimer, "Die Fermente und ihre Wirkungen," second 



edition, 1903; Moore, in "Recent Advances in Physiology and Biochemistry," 



London and New York, 1906; Vernon, "Intracellular Enzymes," London, 



1908; Euler, "General Chemistry of the Enzymes" (translation by Pope), 1912. 



47 



