which are not ferments.  In short, varying our form of expression a little, we may conclude with perfect truth, from the sum total of observed facts, that the yeast which lives in the presence of oxygen and can assimilate as much of that gas as is necessary to its perfect nutrition, ceases absolutely to be a ferment at all.  Nevertheless, yeast formed under these conditions and subsequently brought into the presence of sugar, out of the influence of air, would decompose more in A given time than in any other of its states.  The reason is that yeast which has formed in contact with air, having the maximum of free oxygen that it can assimilate is fresher and possessed of greater vital activity than that which has been formed without air or with an insufficiency of air.  M. Schutzenberger would associate this activity with the notion of time in estimating the power of the ferment; but he forgets to notice that yeast can only manifest this maximum of energy under a radical change of its life conditions; by having no more air at its disposal and breathing no more free oxygen.  In other words, when its respiratory power becomes null, its fermentative power is at its greatest.  M. Schutzenberger asserts exactly the opposite (p. 151 of his work—­ Paris, 1875) [Footnote:  Page 182, English edition], and so gratuitously places himself in opposition to facts.

In presence of abundant air supply, yeast vegetates with extraordinary activity.  We see this in the weight of new yeast, comparatively large, that may be formed in the course of a few hours.  The microscope still more clearly shows this activity in the rapidity of budding, and the fresh and active appearance of all the cells.  Fig. 6 represents the yeast of our last experiment at the moment when we stopped the fermentation.  Nothing has been taken from imagination, all the groups have been faithfully sketched as they were. [Footnote:  This figure is on a scale of 300 diameters, most of the figures in this work being of 400 diameters].

[Illustration with caption:  Fig. 6]

In passing it is of interest to note how promptly the preceding results were turned to good account practically.  In well-managed distilleries, the custom of aerating the wort and the juices to render them more adapted to fermentation, has been introduced.  The molasses mixed with water, is permitted to run in thin threads through the air at the moment when the yeast is added.  Manufactories have been erected in which the manufacture of yeast is almost exclusively carried on.  The saccharine worts, after the addition of yeast, are left to themselves, in contact with air, in shallow vats of large superficial area, realizing thus on an immense scale the conditions of the experiments which we undertook in 1861, and which we have already described in determining the rapid and easy multiplication of yeast in contact with air.

The next experiment was to determine the volume of oxygen absorbed by a known quantity of yeast, the yeast living in contact with air, and under such conditions that the absorption of air was comparatively easy and abundant.