We may still further increase this ratio by making our estimation as soon as possible after the impregnation, or the addition of the ferment.  It will be readily understood why yeast, which is composed of cells that bud and subsequently detach themselves from one another, soon forms a deposit at the bottom of the vessels.  In consequence of this habit of growth, the cells constantly covering each other prevents the lower layers from having access to the oxygen held in solution in the liquid, which is absorbed by the upper ones.  Hence, these which are covered and deprived of this gas act on the sugar without deriving any vital benefit from the oxygen—­a circumstance which must tend to diminish the ratio of which we are speaking.  Once more repeating the preceding experiment, but stopping it as soon as we think that the weight of yeast formed may be determined by the balance (we find that this may be done twenty-four hours after impregnation with an inappreciable quantity of yeast), in this case the ratio between the weights of yeast and sugar is gr/024 yeast/0 gr. 09 sugar=1/4.  This is the highest ratio we have been able to obtain.

Under these conditions the fermentation of sugar is extremely languid:  the ratio obtained is very nearly the same that ordinary fungoid growths would give.  The carbonic acid evolved is principally formed by the decompositions which result from the assimilation of atmospheric oxygen.  The yeast, therefore, lives and performs its functions after the manner of ordinary fungi:  so far it is no longer a ferment, so to say; moreover, we might expect to find it to cease to be a ferment at all if we could only surround each cell separately with all the air that it required.  This is what the preceding phenomena teach us; we shall have occasion to compare them later on with others which relate to the vital action exercised on yeast by the sugar of milk.

We may here be permitted to make a digression.

In his work on fermentations, which M. Schutzenberger has recently published, the author criticises the deductions that we have drawn from the preceding experiments, and combats the explanation which we have given of the phenomena of fermentation. [Footnote:  International Science Series, vol. xx, pp. 179-182.  London, 1876.—­D.  C. R.] It is an easy matter to show the weak point of M. Schutzenberger’s reasoning.  We determined the power of the ferment by the relation of the weight of sugar decomposed to the weight of the yeast produced.  M. Schutzenberger asserts that in doing this we lay down a doubtful hypothesis, and he thinks that this power, which he terms fermentative energy, may be estimated more correctly by the quantity of sugar decomposed by the unit-weight of yeast in unit-time; moreover, since our experiments show that yeast is very vigorous when it has a sufficient supply of oxygen, and that, in such a case, it can decompose much sugar in a little time, M. Schutzenberger concludes that it must then have great power as a ferment, even greater than when it performs its functions without the aid of air, since under this condition it decomposes sugar very slowly.  In short, he is disposed to draw from our observations the very opposite conclusion to that which we arrived at.