FERMENTATION AND DISEASE. 137 



manner. In aerated liquids they flourish without any production of 

 alcohol, but cut off from free oxygen they act as ferments, producing 

 alcohol exactly as the real alcoholic leaven produces it, only less co- 

 piously. For all this knowledge 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 substance. But the substance itself may 

 also have within it, to some extent, the motive power of fermenta- 

 tion. The yeast-plant, as we have learned, is an assemblage of liv- 

 ing 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 liber- 

 ated an approximately equal volume of carbonic acid. He also found 

 that, when ripe fruits were placed in a confined atmosphere, the oxy- 

 gen of the atmosphere was first absorbed, and an equal quantity 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 expired by the fruits, which at the same time lost a 

 portion of their sugar, becoming more aci-d to the taste, though the 

 absolute quantity of acid was not augmented. This was an observa- 

 tion 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 lives, 

 by extracting oxygen from the saccharine juices round them ? This 

 is a question of extreme theoretic significance. It was first answered 

 affirmatively by the able and conclusive experiments of Lechartier 

 and Bellamy, and the answer was subsequently confirmed and ex- 

 plained by the experiments and the reasoning of Pasteur. Berard 

 only showed the absorption of oxygen and the production of car- 

 bonic acid; Lechartier and Bellamy proved the production of alco- 

 hol, thus completing the evidence that it was a case of real fermenta- 

 tion. Influenced by his theoretic views, so full was Pasteur of the 

 idea that the cells of a fruit would continue to live at the expense 

 of the sugar of the fruit, that once in his laboratory, while convers- 

 ing on these subjects with M. Dumas, he exclaimed, " I will wager 

 that if a grape be plunged into an atmosphere of carbonic acid, it 

 will produce alcohol and carbonic acid by the continued life of its 

 own cells that they will act for a time like the cells of the true al- 

 coholic leaven." He made the experiment, and found the result to 



