§ IX.] Acetous fermentation. 87 



vinegar. In the proper temperature, and with free access of 

 atmospheric air, the mother of vinegar developes into the mem- 

 brane described above, and as this takes place the alcohol in 

 solution is converted into acetic acid. 



The various methods used in the arts for the preparation of 

 vinegar, into the details of which we do not here enter, are cul- 

 tures of Micrococcus aceti at the proper temperature, and with 

 exposure to the air under regulations which vary in each par- 

 ticular case. The mixtures from which the vinegar is to be 

 prepared— beer, wine, &c., with addition of previously formed 

 vinegar, have the essential characters of nutrient solutions as 

 described above. The vinegar of commerce is a diluted solution 

 of acetic acid, and contains a larger or smaller number of the 

 Micrococcus aceti. Germs of this organism are also diffused 

 elsewhere, and in particular are never wanting in the vessels 

 used for the preparation and storing of alcoholic fluids. When 

 these turn acid, owing to careless management, it is in part at 

 least owing to the activity of the Micrococcus. M. aceti, like 

 M. Ureae, is as far as we know at present an arthrosporous 

 Bacterium, and resembles the latter in shape (Fig. 10). It con- 

 sists usually, and always in the normal vegetating stage, of 

 cylindrical cells, which are not much longer than broad, and 

 have a transverse diameter of about o-8-i ft. The cells multiply 

 by the usual process of transverse division, and often remain 

 united together in rows forming long filaments ; in older cultures 

 they are often thrust out of the filament but are held together 

 by jelly. With this short-celled Micrococcus-form cell-rows 

 often occur, in which some cells are in the form of long rods, 

 others not only several times longer than broad, but also fusiform 

 and so swollen in a bladder-like manner that their greatest 

 breadth may be more than four times the diameter of the ordinary 

 cells. No one would suppose these inflated cells to belong to 

 the small ones, if they did not usually occur with them, either 

 singly or several together, as members of the same genetic rows 

 and connected with them by a variety of intermediate forms. 



