FERMENTATION. 93 



it can only bring about the detachment of the molecules or 

 bricks of a substance when the motion of the molecules of 

 that substance is started or extended by the action of a 

 certain degree of heat ; thus fermentation will not take place 

 unless the material to be fermented is kept at a temperature 

 of from 10 to 40. This increased temperature acts, pro- 

 bably, in two ways : first, by increasing the motion of the 

 molecules as above stated, and secondly, by enabling the 

 protoplasm to act more energetically, by increasing the rate 

 and extent of molecular motion within the organism itself. 

 The determining motion, according to Bunge, " might pro- 

 ceed from the vital functions of the cell. But it is likewise 

 conceivable that certain substances occur in the cell, and 

 that these substances act in a similar manner to the catalytic 

 bodies in the examples adduced above." Heat and moisture 

 are both necessary factors in all processes of fermentation, 

 but neither of these alone can give rise to it. 



Pasteur, who was really the first to understand this sub- 

 ject so far as to be able to throw light upon it for others, 

 looked upon " fermentation, properly so called, as a chemical 

 phenomenon, co-relative with physiological actions of a pecu- 

 liar nature," the elements in which the peculiar physiological 

 actions were manifested being spoken of as ferments which 

 were not dead albuminoid matter, as held by Liebig and his 

 school, but actually living organisms " of a peculiar nature 

 in this sense, that they have the property of exercising all 

 the functions of their life, not excepting ' vegetative multi- 

 plication,' without necessarily employing the oxygen of the 

 atmospheric air ; ' and he thus generalizes his results : 

 " Guided by all these facts, I have been gradually led to 

 look upon fermentation as a necessary consequence or mani- 

 festation of life when that life takes place without the direct 

 combustion due to free oxygen." This opened up exceed- 

 ingly wide and important questions : Was it possible that 

 all living plant-cells might have the power of inducing 

 fermentation in a more or less marked degree ? and did 

 yeasts differ from other living cells only in the fact that 

 they had more marked powers of acting on certain carbo- 

 hydrates, and of exciting alcoholic fermentation ? Experi- 

 ments on fruit, on barley, on leaves, all went to prove that the 

 elementary cells of plants possessed within themselves this 

 power of inducing fermentation of sugar that was already 



