658 PHYSIOLOGY OF DIGESTION AND SECRETION. 



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 

 conclusion, then the general explanation of fermentation is to be 

 sought in the nature of the enzymatic processes. Within recent 

 years the study of the enzymes has attracted especial attention. 

 A very large literature is developing, and the subject is therefore 

 correspondingly difficult to present in brief compass. The general 

 point of view regarding the mode of action of enzymes that is most 

 frequently met with to-day is that advocated especially by Ostwald. 

 He assumes, reviving an older view (Berzelius), that the ferment 

 actions are similar to those of catalysis. By catalysis chemists 

 designated a species of reaction which is brought about by the mere 

 contact or presence of certain substances, the catalyzers. Thus, 

 hydrogen and oxygen at ordinary temperatures do not combine 

 to form water, but if spongy platinum is present the two gases unite 

 readily. The platinum does not enter into the reaction, at least it 



* Consult Green, "The Soluble Ferments and Fermentations," 1899; 

 Effront, " Enzymes and their Applications" (translation by Prescott), 1902; 

 Oppenheimer, "Die Fermente und ihre Wirkungen," second edition, 1903; 

 and Henri, " Lois generates de Taction des diastases, " 1903. 



