66 MICROBES, FERMENTS, AND MUULDS. 
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, 
