BACTERIA. 57 



Turpin and Kutzing that the acetic acid fermentation is 

 caused by a micro-organism, which Kutzing described and 

 delineated under the name of Ulvina aceti. Starting from 

 this, Pasteur, first in his treatise (1864) and subsequently in 

 his work "Etudes sur le vinaigre" (1868), furnished experi- 

 mental proof of the correctness of this view, and also gave a 

 method, based on the results, for the manufacture of vinegar. 

 He assumed that the acetic acid fermentation was caused by a 

 species of micro-organism which he called Mycoderma aceti. 

 Subsequent research has, however, shown that there are 

 different species of acetic acid bacteria. With Pasteur, 

 therefore, it was not at all a question of the employment of 

 one definite, selected species. His method consists in giving 

 a large surface to the liquid employed two parts of bright 

 wine to one part of wine-vinegar and then sowing on the 

 surface of the mixture a young film consisting of " mother 

 of vinegar." When the temperature, the composition of the 

 liquid, and all other conditions are favourable, the formation 

 of acetic acid will proceed more quickly than in the older 

 Orleans process. The installation is claimed to be cheaper, 

 and the loss of alcohol not greater at all events not to any 

 appreciable extent than in the last-named process. Yet, 

 as far as I have been able to learn, Pasteur's process is never 

 employed. The cause of the uncertainty of the results may 

 be sought in the fact that the composition of the nutritive 

 liquid varies, and especially in the fact that the bacterial 

 culture was not a pure culture, and might, therefore, also 

 contain varieties of bacteria which possessed different pro- 

 perties, required different conditions for their growth, and, con- 

 sequently, would give different products in varying quantities. 

 This will hold good even in those cases in which the composite 

 culture consists only of such varieties which can produce 

 vinegar. As early as 1879 Hansen discovered that at least 

 two distinct species are hidden under the name of Mycoderma 

 aceti, namely, Bacterium aceti and Bact. Pasteurianum ; 

 and he has shown that also in this branch of industry it is 



