200 PASTEUR: THE HISTORY OF A MIND 



Penicillium rapidly suspends its action and becomes inert ; 

 the mycelium of Aspergillus continues a little longer to 

 consume the sugar, but its growth is also soon arrested. 

 Only the mycelium of Mucor endures for several hours 

 this deprivation of air. It becomes foamy as the result 

 of an ebullition, abundant at first then more slow, of 

 bubbles of carbonic acid; and we find in the liquid very 

 perceptible quantities of alcohol. In short, to the com- 

 plete combustion which the mucor gives in contact with 



FIG. 16. Yeast-like forms assumed by Mucor mucedo in the absence 

 of air. 



air, there succeeds, without transition and without ap- 

 parent difficulty, at least in the beginning, a partial 

 combustion in the form of an alcoholic fermentation. 



Singularly, the mycelium of the plant becomes modi- 

 fied under these new conditions of existence; that of the 

 Penicillium remains almost as it was; that of the Asper- 

 gillus segments and in place of the branching filaments 

 has chains of cells. It is in the mycelium of the Mucor 

 that the changes are the most marked. As long as the 

 fungus is living as a mold in free contact with air, its 



