Now that the discovery of ferments and their living nature, and our knowledge of their origin, may have solved the mystery of the spontaneous appearance of fermentations in natural saccharine juices, we may ask whether we must still regard the reactions that occur in these fermentations as phenomena inexplicable by the ordinary laws of chemistry.  We can readily see that fermentations occupy a special place in the series of chemical and biological phenomena.  What gives to fermentations certain exceptional characters of which we are only now beginning to suspect the causes, is the mode of life in the minute plants designated under the generic name of ferments, a mode of life which is essentially different from that in other vegetables, and from which result phenomena equally exceptional throughout the whole range of the chemistry of living beings.

The least reflection will suffice to convince us that the alcoholic ferments must possess the faculty of vegetating and performing their functions out of contact with air.  Let us consider, for instance, the method of vintage practised in the Jura.  The bunches are laid at the foot of the vine in a large tub, and the grapes there stripped from them.  When the grapes, some of which are uninjured, others bruised, and all moistened by the juice issuing from the latter, fill the tub—­where they form what is called the vintage—­they are conveyed in barrels to large vessels fixed in cellars of a considerable depth.  These vessels are not filled to more than three-quarters of their capacity.  Fermentation soon takes place in them, and the carbonic acid gas finds escape through the bunghole, the diameter of which, in the case of the largest vessels, is not more than ten or twelve centimetres (about four inches).  The wine is not drawn off before the end of two or three months.  In this way it seems highly probable that the yeast which produces the wine under such conditions must have developed, to a great extent at least, out of contact with oxygen.  No doubt oxygen is not entirely absent from the first; nay, its limited presence is even a necessity to the manifestation of the phenomena which follow.  The grapes are stripped from the bunch in contact with air, and the must which drops from the wounded fruit takes a little of this gas into solution.  This small quantity of air so introduced into the must, at the commencement of operations, plays a most indispensable part, it being from the presence of this that the spores of ferments which are spread over the surface of the grapes and the woody part of the bunches derive the power of starting their vital phenomena [Footnote:  It has been marked in practice that fermentation is facilitated by leaving the grapes on the bunches.  The reason of this has not yet been discovered.  Still we have no doubt that it may be attributed, principally, to the fact that the interatices between the grapes, and the spaces between the bunch leaves throughout, considerably increase the volume of air