STUDIES ON FERMENTATION. 259 



The conclusions to be drawn from the whole of the pre- 

 ceding facts can scarcely admit of doubt. As for ourselves, we 

 have no hesitation in finding in them the foundation of the 

 true theory of fermentation. In the experiments which we 

 have described, fermentation by yeasty that is to say, by the 

 type of ferments properly so called, is presented to us, in a 

 w^ord, as the direct consequence of the processes of nutrition, 

 assimilation, and life, when these are carried on without the 

 agency of free oxygen. The heat required in the accomplish- 

 ment of that work must necessarily have been borrowed from 

 the decomposition of the fermentable matter, that is from the 

 saccharine substance which, like other unstable substances, 

 liberates heat in undergoing decomposition. Fermentation by 

 means of yeast appears, therefore, to be essentially connected 

 with the property possessed by this minute cellular plant of 

 performing its respiratory functions, somehow or other, with 

 oxygen existing combined in sugar. Its fermentative power — 

 which power must not be confounded with the fermentative 

 activity or the intensity of decomposition in a given time — 

 varies considerably between two limits, fixed by the greatest 

 and least possible access to free oxygen which the plant has in 

 the process of nutrition. If we supply it with a sufficient 

 quantity of free oxygen for the necessities of its life, nutrition, 

 and respiratory combustions, in other words, if we cause it to 

 live after the manner of a mould, properly so called, it ceases to 

 be a ferment, that is, the ratio between the weight of the plant 

 developed and that of the sugar decomposed, which forms its 

 principal food, is similar in amount to that in the case of 

 fungi* On the other hand, if we deprive the yeast of air 



this liquid. It contained 0'3 gramme (4-6 grains) of alcohol, and 

 0-053 gramme (08 grain) of vegetable matter, dried at 100° C. (212° F.). 

 "We ascertained that the spores of the fungus were dead at the moment 

 when the flask was opened. When sown, they did not develop in the 

 least degree. 



* We find in M. Eaulin's Note, already quoted, that "the minimum 

 ratio between the weight of sugar and the weight of organized matter, 

 that is, the weight of fungoid growth which it helps to form, may be 



s 2" 



