STUDIES IN FERMENTATION 69 



by means of a number of organized nitrogenous 

 substances, different from the yeast of beer, pro- 

 vided that they are in a state of decomposition. 

 It is these dead substances which are the ferments. 

 I do not forget, moreover, the experiments of 

 Thenard on the almost constant production of yeast 

 in fermenting fluids. ... But this yeast does not 

 embarrass me; it enters my system. If you admit 

 that it lives you also admit that it dies. Then it 

 is in dying that it acts, as a consequence of the de- 

 composition that it undergoes at this time, and of 

 this Thenard furnishes us the proof." 



This passage read in the light of our present 

 information is most instructive in reflecting the 

 most advanced knowledge of its day. That it con- 

 tains a number of errors both in statement of fact 

 and in conclusions was made apparent by the later 

 observations of Pasteur. Liebig held that albu- 

 minous substances in a state of decomposition im- 

 parted a sort of "molecular movement" whose in- 

 fluence is to break up sugar into alcohol and 

 carbon dioxide, or in the case of putrefaction, to 

 effect destructive changes that give rise to other 

 products. This view was defended by Liebig with 

 energy and ability and it became the most widely 

 accepted doctrine of the time. 



