Page:Popular Science Monthly Volume 5.djvu/561

Rh ale. In the first few years of this century Turpin, and afterward Cagniard-Latour, attempted in vain to prove that such a relation existed; it was always denied that any thing else could be observed in alcoholic fermentation than an operation resembling all those slow decompositions that were classed among fermentations. We have admitted, in our time, that alcoholic fermentation, instead of being an exception, is on the contrary the very type of the phenomena we are treating of; that the yeast-cells, far from being unimportant, take an essential part in it, and that in all fermentations whatever there occur low organizations, microscopic corpuscles, more or less analogous to those of yeast. At least this is the first result of investigations carried on in the past fifteen years by several men of science, among whom in the first rank M. Pasteur is to be cited.

M. Pasteur began the course of his labors in 1858, by the study of alcoholic fermentation. He placed it beyond a doubt that, in the case of grape-juice or beer-wort, as in that of any other saccharine liquid exposed to the air, the more or less rapid production of alcohol is always connected with the production of a microscopic fungus, consisting of rounded globules, a few thousandths of a millimetre in diameter. These globules, known under the name of brewer's yeast, multiply in the fermenting liquid at the expense of the organic matters it contains, and, by the exchanges of growth they give rise to, produce decomposition of the sugar into alcohol and carbonic, succinic, and glyceric acids. These are the four invariable products of alcoholic fermentation. Sugar is the food of the yeast-fungus; these products are its excretions. The laws of the inner mechanism that elaborates them are yet unknown. But every thing leads us to believe that the yeast-cells secrete a substance more or less resembling those that work out the phenomena of digestion in the higher animals. Alcoholic fermentation would thus be a kind of digestion of sugar within the globule.

M. Dumas, who signalized his entrance upon the career of studies in natural science half a century ago, by memorable discoveries in microscopic physiology, has lately returned to researches of the same kind, precisely, in respect to fermentations. In M. Pasteur's laboratory at the Normal School he has taken up investigations on this subject, the results of which, quite lately published, show that the distinguished savant in question has lost neither his cautious diligence in experimental processes, nor his lucid conception in the grasp of principles. He has attempted among other things to determine the decomposing force, the amount of activity, possessed by each cell of the alcoholic ferment. To ascertain this, he measured the quantity of sugar decomposed in a given time by a fixed weight of yeast, and he found—after first establishing that a cubic millimetre of yeast contains about 2,772,000 cells—that the power of a million of cells represents the force capable of decomposing four grains of sugar in an hour. If we attempted according to this estimate to express in figures the number of cells