124 PASTEUR: THE HISTORY OF A MIND 



II 

 THE MYCODERMA OF VINEGAR 



As Pasteur had thought it out, all the work of oxidation 

 was performed by a micro-organism differing from those 

 with which he had been familiar up to this time, in that 

 it is an agent for the transmission of the oxygen of the 

 air to certain substances. These functions make it nec- 

 essary for it to live in contact with the air on the one 

 hand, and with the nutrient substance on the other, and 

 it develops on the surface of the liquid in the form of a 

 delicate veil, smooth and level at first, later in folds, 

 because, when the organisms become too crowded, it is 

 necessary for them to pile up on each other. This form 

 of veil won for this organism the name of Mycoderma 

 aceti, or the mycoderma of vinegar. 



Three things were remarkable about this organism. 

 In the first place, its marked aerobic character. It was 

 the exact antipode of the butyric vibrio, previously dis- 

 covered, and it was to characterize the two so opposite 

 functions of these two organisms that there were created 

 with the collaboration of Chassang, professor of Greek 

 in the Ecole Normale, the two words aerobic and anae- 

 robic. The acetic ferment was also singularly prolific- 

 In 24 hours, it would cover the surface of a vat of any 

 size whatever, with a fine pellicle of cells crowded to- 

 gether, provided that one sowed here and there some 

 cells, as seed. These form islands which become joined 

 in a continuous layer. The cells of the ferment are 

 almost twice as long as broad (5, Fig. 8). It takes 400 

 of them placed end to end, or 800 placed side by side, to 

 make a millimeter. That makes a minimum of 30 

 millions of cells to the square centimeter, or 300 thou- 

 sand millions of cells in a vat with a surface of a square 



