FERMENTS, FERMENTATIONS, AND LIFE. 257 



ferment. To ascertain this, he measured the quantity of 

 sugar decomposed in a given time by a fixed weight of yeast, 

 and he found after first establishing that a cubic mil- 

 limetre of yeast contains about 2,772,000 cells that the 

 power of a million of cells represents the force capable of 

 decomposing four grains of sugar in an hour. If we at- 

 tempted according to this estimate to express in figures the 

 number of cells employed in producing the wine, beer, and 

 cider, consumed every year, as Dumas says, even astrono- 

 mers would shrink from the task. 



This active property of decomposing sugar, and forming 

 alcohol in consequence, does not belong to the cells of 

 brewer's yeast exclusively. Several chemical agents possess 

 the same power, and certain vegetable cells also are adapted 

 to use it. When fruits are placed in a medium filled with 

 oxygen, they absorb this gas, and occasion the release of 

 carbonic acid ; if, on the contrary, they are left in carbonic 

 acid or any other inert gas, they effect the production of 

 alcohol. The fruits remain firm and hard, without suffer- 

 ing any external change, but the sugar they contain is 

 transformed in part into alcohol. How is this phenomenon 

 to be explained ? In common air, the cell of the fruit is fed 

 by oxygen ; if this gas is withheld, it is forced to borrow the 

 materials of nutrition from the fluids that moisten it, that 

 is, from the saccharine juice, and then the latter is decom- 

 posed. Pasteur has noted that a similar alcoholic fermen- 

 tation takes place in other vegetable organs, in leaves, for 

 instance, and in every case he has proved that the phenom- 

 enon is due to the cells of the vegetables alone, and not 

 to yeast-globules. Far from throwing any doubt on the 

 physiological doctrine of fermentation, these singular facts 

 agree in lending it support, by giving it deeper and more 

 general application. 



We have seen that the fermentation of sugar yields 

 alcohol. The latter, brought in contact with certain porous 

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