304 ACETIC FERMENTATION 



occurred. Nevertheless, more than one opinion was rife as to the mode of action 

 of this mucinous skin. 



Berzelius, in 1829, on the basis of his theory of catalytic action, ascribed the 

 potency of this skin in acetic fermentation to the acetic acid " enclosed within 

 its pores." Ten years later, and two years after the appearance of Kiitzing's 

 work which, being out of harmony with the spirit of the age, was consequently 

 disregarded Liebig published his theory of acetic fermentation, in which the 



" mother of vinegar " was classed along- 

 side platinum-black, their mode of 

 action being defined as identical and 

 of a purely chemical nature. 



Owing to the endeavours of Pas- 

 teur, the theory promulgated by Kiit- 

 zing was experimentally shown to be 

 correct, and the true import of the 

 vinegar-mother once more recognised. 

 It would, however, be going too far to 

 also credit the French physiologist with 

 having recognised acetic fermentation 

 as a purely physiological process ; for 

 remarkable as it may now appear 

 to us Pasteur, with his followers, 

 stopped half-way and defined the vine- 

 gar fungus as " acting after the manner 

 of spongy platinum." He characterised 

 the skin-like zoogloea of the fission 

 fungus in question as " vegetations en- 

 dowed with the remarkable peculiarity 

 of retaining the oxygen of the air and 

 condensing it after the manner of 

 spongy platinum, by inducing the com- 

 bustion of alcohol and acetic acid." VV. 

 VON KNIERIEM and AD. MAYER (I.) 

 share theci'edit of having convincingly 

 proved, in 1873, that the oxidation of 

 alcohol by means of platinum-black 

 FIG oo-Bacturiiuniiceti cannot be classed along with the fer- 



Filamentous cells of unusual form from cultures mentatk* setup by the "mother of 

 (several day sold) on wort and on" doppel- bier" Vinegar. Platinum - black OXldlSCS 



at 39-4i c. Magn. 1000. (.(fter Hamm.) both concentrated and dilute alcohol, 



whereas, according to the experience 



of vinegar-makers, acetic fermentation cannot proceed in presence of more 

 than 14 per cent, of alcohol. Moreover, with regard to temperature, highly 

 impoi'tant differences touching the very existence of \ the question are 

 observed. Thus, whereas acetic fermentation proceeds most satisfactorily at 

 about 35 C. and is arrested altogether at 40 C., the energy of the oxidation 

 effected by platinum -black (starting at 35 C.) increases as the temperature 

 rises, and may become so violent that the alcohol ignites explosively and burns 

 away to water and carbon dioxide. Hence the composition of the (by no means 

 uniform) oxidation products thus formed differs greatly from those obtained 

 from acetic fermentation. 



This latter process, whose purely physiological nature was placed beyond 

 doubt by these investigations, was examined more minutely by A. J. BROWN (III.) 

 in 1886. Meanwhile, Hansen's discovery of the existence of at least two species 



