66 MICBOBES, FERMENTS, AND MOULDS. 



CHAPTER II. 



FERMENTS AND ARTIFICIAL FERMENTATIONS. 



I. WHAT is FERMENTATION ? 



CHEMISTS define fermentation in these words : " Fer- 

 mentation takes place wherever an organic compound 

 undergoes changes of composition, under the influence 

 of a nitrogenous organic substance called a ferment, 

 which acts in small quantities and yields nothing to 

 the fermented substance " (A. Gautier). 



This nitrogenous substance, termed a ferment, is 

 regarded by naturalists as an organized living being, 

 either animal or vegetable. This was demonstrated 

 by the researches of Cagnard de La Tour, of Turpin, 

 of Dumas, and more recently by the splendid achieve- 

 ments of Pasteur. It is now proved that the artificial 

 fermentation which takes place .in the manufacture 

 of wine, beer, etc., is produced by small microscopic 

 plants, called ferments or yeast. 



The chemical transformation resulting from them 

 might be obtained without the intervention of yeast, 



