The more we advance, the more clearly we are able to detect these differences.  M. Dumas has insisted on the fact that the ferments of fermentation proper multiply and reproduce themselves in the process whilst the others are destroyed. [Footnote:  “There are two classes of ferments; the first, of which the yeast of beer may be taken as the type, perpetuate and renew themselves if they can find in the liquid in which they produce fermentation food enough for their wants; the second, of which diastase is the type, always sacrifice themselves in the exercise of their activity.” (Dumas, Comptes rendus de l’Academie, t. lxxv., p. 277, 1872.)] Still more recently M. Muntz has shown that chloroform prevents fermentations proper, but does not interfere with the action of diastase (Comptes rendus, 1875).  M. Bouchardat had already established the fact that hydrocyanic acid, salts of mercury, ether, alcohol, creosote, and the oils of turpentine, lemon, cloves, and mustard destroy or check alcoholic fermentations, whilst in no way interfering with the glucoside fermentations (Annales de Chimie et de Physique. 3rd series, t. xiv., 1845).  We may add in praise of M. Bouchardat’s sagacity, that that skilful observer has always considered these results as a proof that alcoholic fermentation is dependent on the life of the yeast-cell, and that a distinction should be made between the two orders of fermentation.

M. Paul Bert, in his remarkable studies on the influence of barometric pressure on the phenomena of life, has recognized the fact that compressed oxygen is fatal to certain ferments, whilst under similar conditions it does not interfere with the action of those substances classed under the name of soluble ferments, such as diastase (the ferment which inverts cane sugar) emulsin and others.  During their stay in compressed air, ferments proper ceased their activity, nor did they resume it, even after exposure to air at ordinary pressures, provided the access of germs was prevented.

We now come to Liebig’s principal objection, with which he concludes his ingenious argument, and to which no less than eight or nine pages of the Annales are devoted.

Our author takes up the question of the possibility of causing yeast to grow in sweetened water, to which a salt of ammonia and some yeast-ash have been added—­a fact which is evidently incompatible with his theory that a ferment is always an albuminous substance on its way to decomposition.  In this case the albuminous substance does not exist; we have only the mineral substances which will serve to produce it.  We know that Liebig regarded yeast, and, generally speaking, any ferment whatever, as being a nitrogenous, albuminous substance which, in the same way as emulsin, for example, possesses the power of bringing about certain chemical decompositions.  He connected fermentation with the easy decomposition of that albuminous substance, and imagined that the phenomenon occurred in the following