PASTEUR ON FERMENTATION. 713 



should we not have discovered the cause of this important phe- 

 nomenon ? Tlie real causes of phenomena escape us. In sound phi- 

 losojjhy the word cause should be reserved for the divine impulse 

 which formed the universe. We can detect only correlations. One 

 phenomenon succeeds another, and cannot exist without its manifesta- 

 tion ; by abuse of language we then say there is relation of cause and 

 effect. 



Well, it is so. This phenomenon is general. Yes, when there is 

 life without air, there is fermentation, and when there is fermentation 

 there is life without air. 



We all know that fruits detached from the tree and exposed to 

 the air live, if we may so express it, like animals and certain inferior 

 plants, for they absorb the free oxygen which surrounds them, and 

 exhale a volume of carbonic-acid gas about equal to that of the oxy- 

 gen which is introduced into their cells to produce in them certain 

 manifestations of life, for the fruit continues to ripen. That being 

 admitted, let us place a fruit, not in tlie air, but in carbonic-acid gas. 

 Of two things, one, life, or, if you prefer, a certain chemical process, 

 will go on in the cells of the fruit, or all chemical change will be ab- 

 solutely suspended. If the latter hypothesis should be realized the 

 fruit would remain inert, intact, and we should there have an admi- 

 rable means for the preservation of fruit. But thit is not the case : 

 experiment proves that it is tlie first hypothesis which is realized ; tlie 

 simplest observation shows that fruit plunged into an atmosphere of 

 carbonic-acid gas is modified more or less profoundly. Plums, for 

 example, become hard and woody, and the grape takes exactly the 

 flavor of the vintage. Where, then, have the cells of the fruit, in order 

 to accomplish this chemical work, which, like all other work, requires 

 the consumption of heat where, I repeat, have they found tlie heat 

 needed for these modifications, for this sort of life continued imder 

 abnormal conditions ? Certainly it does not come from combustion, 

 due to free oxygen, as when the fruit is suspended in ordinary air, for 

 in this atmosphere of carbonic-acid gas there is no free oxygen. This 

 heat, indispensable to the phenomena which observation detects, is 

 furnished by the decomposition of sugar. The position is the same as 

 in the case of the decomposition of sugar in the presence of yeast-cells 

 living without air. This decomposition of the sugar is manifested in 

 the fruit by the production of alcohol and of carbonic acid. Here the 

 ferment is the cell of the parenchyma of the fruit. There is in this 

 cell a life kept up, or a chemical process accomplished, without air ; 

 according to our theory, fermentation should be present there, and ex- 

 periment shows that it is. The theory, then, receives from this fact 

 an extension and a generalization which increase and strengthen it. 



That is why in my last communication to the Academic des Sci- 

 ences I expressed myself thus: "Every being, every organ, every 

 cell which has the faculty of accomplisliing a chemical process with- 



