402 THE BEGINNINGS OF LIFE. 



process two things are necessary : in the first place,, 

 there must be a fermentable substance a body capable of 

 undergoing chemical change and, in the second place, 

 there must be & ferment, or substance capable of initiat- 

 ing such a change. According to MM. Pelouze and 

 Fremy, c the decomposition of organic substances under 

 the influence of a body which acts only by its mere pre- 

 sence is called fermentation.' What, then, is the nature 

 of the ferment ? It has generally been regarded as some 

 nitrogenous substance, belonging to the albumenoid type, 

 though subject to much variation in actual composition. 

 Gerhardteven says that c a ferment is not a bodysu? generis, 

 but rather any substance in a state of decomposition.' 



In the opinion of some chemists followers of 

 Gay-Lussac the mere presence of the ferment in com- 

 pany with the fermentable substance is not sufficient. 

 Even its activity must be excited before it can act 

 upon the fermentable substance: a result generally 

 brought about by the action of the oxygen contained in 

 the air with which the ferment is in contact *. But 

 according to other chemists and more especially to 

 Liebig 2 it is only necessary to have a body which 

 decomposes, perhaps spontaneously, in the presence of 

 another (fermentable substance) whose elements are 

 held together by a feeble affinity. The more change- 

 able substance, by virtue of its own inherent instability, 



1 So that, as Gerhardt says, ' L'oxygbne de 1'air, comme nous 1'avons 

 <djt, est done le primum movens des fermentations.' Loc. cit. p. 540. 

 9 ' Annales de Chimie et de Physique,' 2nd serie, t. Ixxi. p. 1 78. 



