530 THE AIR AND LIFE, 



fermentation. They produce fermentation only when in a medium 

 devoid of oxygen, and M. Pasteur was fully justified in saying that fer- 

 mentation is a consequence of life without air. What, then, occurs in a 

 fermenting medium'? A particular kind of microbe (each kind of fer- 

 mentation being caused by a special microbe) transported by air or water, 

 or intentionally introduced, has beeu living in that medium for some 

 timeonthe oxygen therein contained. After a time, the free oxygen hav- 

 ing been consumed by the microbe, the supply is practically exhausted. 

 Some oxygen, however, is left in the medium, not free, but in combi- 

 nation with elements of the latter; and the microbe has the power of 

 extracting or decoinbining that gas and of applying it to its own use. 

 As this can only be done by destroying an existing chemical combina- 

 tion, the elements are released and, in the process of disengagement? 

 cause the characteristic phenomena of fermentation. Thus, in the alco- 

 holic fermentation of saccharine substances, as cane or grape sugar, the 

 microbe removes from the sugar a portion of its component oxygen, 

 thus decomposing it into free carbonic acid and alcohol. This is 

 one illustration out of a hundred useless to enumerate. All experiments 

 prove that wherever fermentation takes place a microbe is present, 

 which, unable to find its requisite sui)ply of oxygen, takes it from the 

 surrounding substances by decomposing them and changing them into 

 new compounds containing in part the same elements as the origiiuil, 

 but differently united. Thus those microbes that are apparently most 

 averse to the contact of air, the anaerobies, breathe oxygen like all 

 other beings. We nuiy practically coiu-lude that life is not impossible 

 in the absence of free oxygen, and at the same time we may assert that 

 wherever there is life there is some means by which the living being 

 can procure its supply of oxygen. The apparent exception in the case 

 "of the anaerobic microbes is therefore no exception. 



Between the essentially anaerobic microbes and those that are aero- 

 bic, that require free oxygen, there are of course all the stages of 

 transition and it would not be possible here to enter into all the partic- 

 ulars by which to show that differences exist only in degree. A 

 reminder that vegetable cells, by reason of their aptitude to cause 

 alcoholic fermentation, for instance, are both aerobic and anaerobic 

 will suffice. " Let us put a beet in carbonic acid," says Mr. Duclaux, 

 "we shall see it make alcohol. Let us also put cherries, plums, apples, 

 any kind of sweet fruit, whole sacchariferous plants, again their sugar 

 is partly turned into alcoh(d and carbonic acid. Under these novel 

 conditions of life they in nowise differ from yeast, except that they are 

 less able to endure life without air, that they do not carry fermentation 

 so far, and that life ceases before a complete transformation of their 

 sugar is accomplished. But these are mere differences in degree." We 

 shall be less surprised at these differences if we recall the discoveries 

 of Paul Bert, mentioned above, for we found that even animal tissues 

 are anaerobic. Did we not see that tissues are killed by free oxygen 

 dissolved in the serum of blood, and that they derive no advantage from 



