410 THE BEGINNINGS OF LIFE. 



some of the beech-wood shavings which had been used 

 uninterruptedly for twenty-five years j and in reply to 

 my enquiry whether the Mycoderma acett took part in 

 the production of vinegar, he states that, so far as 

 can be seen, the shavings that have been thirty years 

 in use are quite free from the fungus V Although, 

 therefore, the vinegar-plant is capable of causing the 

 conversion of alcohol into acetic acid, this conversion 

 can be otherwise achieved without the intervention of 

 a living organism. The process is one of oxidation 

 merely, so that even when it does take place by the 

 agency of the vinegar-plant, the effective action is in 

 all probability none the less purely chemical in nature 2 . 

 Baron Liebig says : c Analyses of the air discharged 

 from the vessels where the vinegar is made, show that 

 the oxygen consumed in the oxidation of alcohol is 

 taken from the air, so that the only part taken by 



1 It appears, however, that 'the production of the fungus is a continual 

 source of hindrance in factories where beer-wort is used [instead of 

 dilute alcohol], since the interstices of the wood shavings are gradually 

 stopped up by its growth, and thus free circulation of air is prevented 

 so far as to stop the formation of vinegar.' 



2 The Mycoderma aceti is, also, only an occasional instrument in 

 bringing about the acetous fermentation ; it is not a necessary concom- 

 itant, as yeast-cells seem to be of the vinous fermentation. The acetic 

 fermentation may occur without the presence of the vinegar-plant, 

 though the vinous fermentation never occurs without the appearance of 

 yeast. When produced, yeast is, as we all know, capable of initiating 

 the vinous fermentation in other suitable liquids, though the vinous 

 fermentation is also capable of originating without the influence of 

 pre-existing yeast. In fermentations which commence in this way yeast 

 arises de novo, as one of the results of the process. (See Pouchet's 

 ' Nouvelles Experiences,' Paris, 1864, pp. 190-192.) 



