256 NATURE AND LIFE. 



years by several men of science, among whom in the first 

 rank Pasteur is to be cited. 



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 con- 

 nected with the production of a microscopic fungus, consist- 

 ing 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 ex- 

 changes of growth they give rise to, produce decomposi- 

 tion 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-fun- 

 gus; 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. 



Dumas, who signalized his entrance upon the career of 

 studies in natural science half a century ago, by memo- 

 rable discoveries in microscopic physiology, has lately re- 

 turned to researches of the same kind, precisely, in respect 

 to fermentations. In 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 dis- 

 tinguished savant in question has lost neither his cautious 

 diligence in experimental processes, nor his lucid concep- 

 tion 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 



