72 ENZYMES OR SOLUBLE FERMENTS. 



the fermentation the interesting question at once arose as to how the 

 known cause produces the observed effect, and to this question many 

 answers have been given of which the following are the more im- 

 portant. 



Liebig regarded the ferments as substances in a state of progressing 

 decomposition during which the equilibrium of their constituents is 

 upset and a rapid motion of their minuter parts established. When 

 brought into contact with other decomposable substances the motion 

 of the ferment's particles is communicated to the former, whereupon 

 it also undergoes a decomposition resulting in the formation of the 

 simpler products which make their appearance and are characteristic 

 of the fermentation. According to this view the organised nature of 

 the yeast-cells is left out of account and the phenomena attributed 

 entirely to the purely chemical decomposition of their constituent 

 substance, set going at the outset by oxygen 1 . Pasteur regarded 

 alcoholic fermentation as indissolubly connected with the vegetative 

 growth, multiplication, and metabolism of the yeast-cell. According 

 to this view sugar is the food-stuff out of which the organism obtains 

 the material requisite for its metabolism and growth, the products 

 of the fermentation being thus as it were the excretionary residues 

 of the metabolised food 2 . A third view attributes the fermentative 

 decomposition to the production by the organised ferments of soluble 

 unorganised enzymes to whose activity the decomposition is due. This 

 view received its chief support from the discovery that a part at least 

 of the change which sugar undergoes in presence of yeast may be 

 obtained by means of the soluble enzyme ' invertin ' which can readily 

 be extracted from the dead cells 3 . But as yet all efforts to obtain an 

 enzyme capable of carrying the decomposition beyond the initial stage 

 of inversion have been fruitless. According to von Nageli the living 

 substance of the organised cell is to be regarded as being in continuous 

 and rapid molecular vibration, and the decomposition of the fermentable 

 substance as the result of the direct transference of these vibrations to 

 this substance, by means of which its equilibrium is upset and it is 

 split up into simpler and therefore more stable products 4 . To discuss 

 the merits of these various theories and the experiments upon which 

 they are based is quite impossible within any reasonable limits of 



1 Ann. d. Chem. u. Pharm. Bd. xxx. (1839), Sn. 250, 363. Stahl in 1734 had 

 expressed practically identical views. 



2 This view was keenly attacked by Liebig, Ann. d. Chem. u. Pharm. Bd. CLIII. 

 (1870), Sn. 1, 137. See Pasteur in reply, Ann. Chim. Phys. 4 Ser. T. xxv. (1872), 

 p. 145. 



3 The inverting power of yeast was first stated by Dubrunfaut in 1847. 

 Berthelot obtained invertin in solution in 1860 and Hpppe-Seyler prepared it in the 

 form of a soluble powder in 1871. See references on p. 71. 



4 Theorie der Gcihrung, Miinchen, 1879. 



