94 MICRO-ORGANISMS AND FERMENTATION. 



(beechwood shavings). The species occurring in this process 

 have been the subject of a far-reaching investigation by 

 Henneberg. 



Whilst Pasteur does not explicitly maintain in his memoir 

 that the oxidation of alcohol to acetic acid brought about by 

 bacteria is a purely physiological process, Adolf Mayer ex- 

 pressed this opinion, the correctness of which he confirmed by 

 proving that the vinegar film exercises its greatest activity 

 at 35 C., and that it ceases to react at 40 C., and further that 

 the film cannot react on more than 14 per cent, alcohol. The 

 purely chemical action of platinum black on alcohol presents 

 a contrast, for it is able to react at high temperatures and 

 with higher concentrations. 



Pasteur showed that the acetic acid generated by the 

 oxidation of alcohol is transformed, if the oxidation is con- 

 tinued, into carbon dioxide and water. This has recently been 

 confirmed by Adrian J. Brown. 



A few species are able to bring about other decompositions, 

 owing to their strong oxidising power e.g., the formation of 

 butyric acid from butyl alcohol, gluconic acid from glucose 

 a few, again, have the power of inverting sugar (Bact. aceti and 

 Bact. xylinum). 



An important advance was made in our knowledge of 

 acetic bacteria when Buchner and Meisenheimer, as well as 

 Herzog, proved that this remarkable fermentation is brought 

 about by the activity of an enzyme. The cells may be killed 

 with acetone, and then treated in the same way as the alcohol 

 yeasts (see Chap, v.), and it can then be shown that, after 

 evaporating the liquid, the residue can bring about the 

 acetic fermentation, although it contains no living cells. By 

 this discovery the real nature of the fermentation becomes 

 clear. Like the alcoholic fermentation, it is caused by an 

 enzyme, which may react independently of the living cell 

 that brought it into existence. 



These bacteria grow vigorously in many nutritive fluids 

 e.g., in dextrose solution with peptone and salts. The presence 

 of alcohol is not an essential condition of their existence, 

 and, indeed, more than 4 per cent, of alcohol acts restrict! vely 

 on their growth. 



