126 PASTEUR: THE HISTORY OF A MIND 



attributes of life, but the idea of disease in a creature so 

 small, was none the less original. It was the first time 

 that it had presented itself. Since then, it has been 

 greatly developed. 



On the contrarj^ sometimes this ferment, instead of 

 being arrested half way, goes beyond the acetic acid 

 stage, exactly, again, like the platinum black, and instead 

 of acetic acid, yields water and carbonic acid. Then it 

 consumes the acetic acid which it has formed, and here 

 again we have the first example of the ability of a living 

 organism under certain conditions to destroy a product 

 which under other conditions it has manufactured. The 

 organism consumes the acetic acid when there is no alco- 

 hol at its disposal, that is to say, it consents, when it is 

 starving, to touch a food which it scorns and rejects in 

 other circumstances, and which thus has accumulated 

 in the ambient liquid. But this acetic acid is its second 

 choice of food, and it abandons it in favor of alcohol as 

 soon as it has the opportunity. 



Curious, is it not, this choice of food in the world of 

 infinitesimal organisms! What prevents us from seeing 

 therein an act of volition or of instinct? Observe that it 

 is an entirely different thing from finding that each organ- 

 ism has its own food material, that the yeasts, for ex- 

 ample, can obtain nourishment only from sugar. The 

 acetic ferment can make a choice, and show preferences: 

 it has free will. I know well that it is governed by its 

 needs, but how many acts of volition have as a cause, 

 though often obscure, only that of satisfying needs? 

 Let us not insist upon this point, however, but confine 

 ourselves to noting with what care Pasteur sought by 

 their study, as soon as micro-organisms had brought 

 him into contact with life, new light on the physiology 

 of the higher organisms. He did not fail to compare his 

 acetic ferment, the agent of oxidation, with the red cor- 



