HIS LIFE AND LABOURS. 185 



found it to be the work of a minute fungus, the My- 

 coderma aceti, which, requiring free oxygen for its 

 nutrition, overspreads the surface of the fermenting 

 liquid. By the alcoholic ferment the sugar of the 

 grape-juice is transformed into carbonic acid gas and 

 alcohol, the former exhaling, the latter remaining in 

 the wine. By the Mycoderma aceti the wine is, in its 

 turn, converted into vinegar. Of the experiments made 

 in connection with this subject one deserves special 

 mention. It is that in which Pasteur suppressed all 

 albuminous matters, and carried on the fermentation 

 with purely crystallisable substances. He studied the 

 deterioration of vinegar, revealed its cause, and the 

 means of preventing it. He defined the part played 

 by the little eel-like organisms which sometimes swarm 

 in vinegar-casks, and ended by introducing important 

 ameliorations and improvements in the manufacture of 

 vinegar. The discussion with Liebig and other minor 

 discussions of a similar nature, which M. Kadot has 

 somewhat strongly emphasized, I will not here dwell 

 upon. 



It was impossible for an inquirer like Pasteur to 

 evade the question Whence come these minute 

 organisms which are demonstrably capable of producing 

 effects which constitute the bases of industries whereon 

 whole populations depend for occupation and suste- 

 nance? He thus found himself face to face with the 

 question of " spontaneous generation," to which the 

 researches of Pouchet had just given fresh interest. 

 Trained as Pasteur was in the experimental sciences, 

 he had an immense advantage over Pouchet, whose 

 culture was derived from the sciences of observation. 

 One by one the statements and experiments of Pouchet 

 were explained or overthrown, and the doctrine of spon- 



