There should be nothing very surprising in the fact that fermentation can originate in fruits and form alcohol, without the presence of yeast, if the fermentation of fruits were not confounded completely with ordinary alcoholic fermentation, yielding the same products and in the same proportions. It is through the misuse of words that the fermentation of fruits has been termed _alcoholic_, in a way which has misled many persons.[132] In this fermentation, neither alcohol nor carbonic acid gas exists in those proportions in which they are found in fermentations produced by yeast; and although we may determine in it the presence of succinic acid, glycerine, and a small quantity of volatile acids,[133] the relative proportions of these substances will be different from what they are in the case of alcoholic fermentation. § III.—Reply to certain Critical Observations of the German Naturalists, Oscar Brefeld and Moritz Traube. The essential point of the theory of fermentation, which we have been concerned in proving in preceding paragraphs, may be briefly put in the statement that ferments, properly so called, constitute a class of beings possessing the faculty of living out of contact with free oxygen; or, more concisely still, we may say, fermentation is a result of life without air. If our affirmation were inexact, if ferment-cells did require for their growth or for their increase in number or weight, as all other vegetable cells do, the presence of oxygen, whether gaseous or held in solution in liquids, this new theory would lose all value, its very _raison d’être_ would be gone, at least as far as the most important part of fermentations is concerned. This is precisely what M. Oscar Brefeld has endeavoured to prove, in a Memoir read to the Physico-Medical Society of Wurzburg, on July 26th, 1873, in which, although we have ample evidence of the great experimental skill of its author, he has, nevertheless, in our opinion, arrived at conclusions entirely opposed to fact. “From the experiments which I have just described,” he says, “it follows, in the most indisputable manner, that _a ferment cannot increase without free oxygen_. Pasteur’s supposition that a ferment, unlike all other living organisms, can live and increase at the expense of oxygen held in combination, is, consequently, altogether wanting in any solid basis of experimental proof. Moreover, since, according to the theory of Pasteur, it is precisely this faculty of living and increasing at the expense of the oxygen held in combination that constitutes the phenomenon of fermentation, it follows that the whole theory, commanding though it does such general assent, is shown to be untenable; it is simply inaccurate.”