742 PHYSIOLOGY OF DIGESTION AND SECRETION. 



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 in yeast, the process of putrefaction, etc. 

 Naturally very many theories have been proposed regarding the 

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

 ment 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 which 

 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 

 ferments, such as pepsin, trypsin, etc., which later were generally 

 designated as enzymes (Kuhne). The separation appeared to be 

 entirely satisfactory until Buchner (1897) showed that an unor- 

 ganized ferment, an enzyme (zymase) capable of producing alcohol 

 from sugar, may be extracted from yeast cells. Later the same 

 observer (1903) succeeded in extracting enzymes from the lactic- 

 acid-producing bacteria and the acetic-acid-producing bacteria 

 which are capable of giving the same reactions as the living bacteria. 

 These discoveries indicate clearly that there is no essential difference 

 between the activity of living and non-living ferments. The so- 

 called organized ferments probably produce their effects not by 

 virtue of their specific life-metabolism, but by the manufacture 

 within their substance of specific enzymes. If we can accept this 



* 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. 



