262 FRAGMENTS OF SCIENCE. 



less copiously. For the right apprehension of all these 

 facts we are indebted to Pasteur. 



In the cases hitherto considered, the fermentation 

 is proved to be the invariable correlative of life, being 

 produced by organisms foreign to the fermentable sub- 

 stance. But the substance itself may also have within 

 it, to some extent, the motive power of fermentation. 

 The yeast-plant, as we have learned, is an assemblage 

 of living cells; but so at bottom, as shown by Schleiden 

 and Schwann, are all living organisms. Cherries, 

 apples, peaches, pears, plums, and grapes, for example, 

 are composed of cells, each of which is a living unit. 

 And here I have to direct your attention to a point of 

 extreme interest. In 1821, the celebrated French 

 chemist, Berard, established the important fact that all 

 ripening fruit, exposed to the free atmosphere, absorbed 

 the oxygen of the atmosphere and liberated an approxi- 

 mately equal volume of carbonic acid. He also found 

 that when ripe fruits were placed in a confined atmos- 

 phere, the oxygen of the atmosphere was first absorbed, 

 and an equal volume of carbonic acid given out. But 

 the process did not end here. After the oxygen had 

 vanished, carbonic acid, in considerable quantities, 

 continued to be exhaled by the fruits, which at the 

 same time lost a portion of their sugar, becoming 

 more acid to the taste, though the absolute quantity 

 of acid was not augmented. This was an observation 

 of capital importance, and Berard had the sagacity to 

 remark that the process might be regarded as a kind of 

 fermentation. 



Thus the living cells of fruits can absorb oxygen 

 and breathe out carbonic acid, exactly like the living 

 cells of the leaven of beer. Supposing the access of 

 oxygen suddenly cut off, will the living fruit-cells as 

 suddenly die, or will they continue to live as yeast 



