CHAPTER XXXVII. 



ACETIC FERMENTATION. 



209. Discovery of the Acetic Acid Bacteria. 



IF beer, wine, or other similar alcoholic liquids, are left to stand 

 exposed to the air, they will, at the end of a few days, become 

 covered with a tough, mucinous (usually smooth) skin or film. 

 The alcohol gradually disappears, and, in approximately the same 

 ratio, the presence of acetic acid makes itself evident : the beer, 

 &c., is converted into vinegar. It has been known from the 

 earliest times that an unsoured sample of beer, wine, or the like 

 can be quickly turned into vinegar by the addition of a small 

 quantity of such skin. This latter was regarded as the carrier of 

 the vinegar fermentation, and consequently received the name of 

 "mother of vinegar" (Fr. mere de vinaigre, Ger. Essigmutter}. 

 The first botanical investigation of this substance was made in 

 1822 by PERSOON (I.), who described the organised skin develop- 

 ing on various liquids, and gave it the general name of My co- 

 derma, i.e. mucinous skin or fungoid skin, but never contemplated 

 the existence of any direct connection between acetic fermentation 

 and the development of such a structure. 



This was reserved for the German algologist FR. KUTZING (I.). 

 In his treatise on this subject, published in 1837, he showed, 

 without, apparently, being acquainted with the labours of his 

 predecessor that the "mother of vinegar" is constructed of a 

 number of minute dot-like organisms (which we now call bacteria), 

 arranged together in the form of chains. These he classified as 

 algae, and named them Ulvina aceti, and asserted quite positively 

 that alcohol is converted into acetic acid by the vital activity of 

 these organisms. 



Kiitzing's results, however, attracted but little notice, because, 

 two years after their publication, LIEBIG (III.) appeared on the 

 scene with his theory of acetic fermentation (which will be de- 

 scribed in a subsequent paragraph), in which no mention was 

 made of the potency of living organisms, but the "mother of 

 vinegar " was asserted to be a formation devoid of life : a struc- 

 tureless precipitate of albuminous matter. Only one of the 

 reasons put forward by the German chemist in support of this 

 view, which he stubbornly upheld, will be mentioned here, and 

 that merely as a curiosity. The Dutch chemist, G. MULDER (III.), 



384 



