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 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 developing on various liquids, and gave it the 

 general name of Mycoderma, 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 algse, 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 described 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 structureless 

 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.), celebrated as a chemical expert on wine, subjected the " mother of 

 vinegar" to chemical analysis, and, because he failed to discover the presence 

 of any ash constituents, thought that it must be regarded as a compound of 

 protein and cellulose. Mulder's statement was refuted in 1852 by R. THOMSON 

 (I.), who showed that a sample (but by no means a pure culture) of "mother 

 of vinegar" contained 94.53 per cent, water, 5.134 per cent, organic matter, and 

 0.336 per cent. ash. 



The diffusion of new light on this matter was reserved for PASTEUR (XIII.). 

 Taking up anew the question of the origin of acetic fermentation examined by 

 Kutzing merely from the purely botanical side, and that only cursorily he 

 controverted the opinions of the chemists, and proved, in 1864, that this 

 fermentation also is a physiological process, whose inception and maintenance 

 is bound up with the vital activity of minute fungoid organisms, to which he 



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