ACETIC-ACID BACTERIA 467 



the sides of the vessel. The pellicles formed are zoogleal masses 

 in which the individual bacteria are held together by a plasmatic, 

 gelatinous substance. In the case of Bacterium aceti the latter is 

 not stained by iodine solution, while in the other two vinegar bacilli 

 it is stained blue. The bacterial protoplasm proper of all three 

 species stain yellow with iodin solution. Another acetic-acid bac- 

 terium, commonly known in England as vinegar plant, has been 

 described by Brown as the Bacterium xylinum. It forms tough, 

 leathery, thick zoogleal masses. The three species of Hansen also 

 show marked differences in pure cultures on solid media (wort 

 gelatin). Bacterium aceti forms very delicate, rosette-like colonies; 

 Bacterium Pasteurianum develops colonies with a smooth, round 

 periphery and folded surface, and Bacterium Kuetzingianum shows 

 smooth colonies without any surface folds. All three types are short, 

 rather thick bacilli, but they exhibit considerable pleomorphism 

 under various conditions. Their optimum temperature of growth 

 lies between 34 and 42 C., and they cease multiplication between 

 5 and 7 C. When raised at a temperature of 34 C. the Bacterium 

 Pasteurianum forms chains of bacilli which are about 2 micra long 

 and 1 micron thick. If these are transferred to a fresh medium kept 

 at 40.5 C., long filaments are formed in which no dividing lines can 

 be seen, and which reach a size of from 40 to 200 micra. If these 

 are again transplanted to a fresh medium kept at 34 C., globular or 

 elliptical swellings are formed in the threads, and these later break up 

 into short rods and pear-shaped or globular cells, sometimes measuring 

 10 micra in diameter. The other two acetic-acid bacilli of Hansen 

 under similar conditions likewise show much pleomorphism and even 

 develop branched forms. 



The conversion of alcohol into acetic acid is a process of oxidation, 

 represented by the formula: 



C 2 H 6 + 2 = C 2 H 4 2 + H 2 0. 



Alcohol. Oxygen: Acetic acid. Water. 



In the manufacture of vinegar from alcoholic liquids, such as wine, 

 beer, and cider, provision must always be made that the air has free 

 access to the fermenting fluid. This is accomplished by either 

 allowing air to enter the barrels from one side and to escape from 

 another, or by leading the fermenting fluid through barrels, vats, 

 or tubes containing masses of wood shavings. This arrangement 

 spreads the fluid over a large surface and allows it to mix thoroughly 

 with air. Pure cultures of acetic-acid bacteria are not yet generally 

 used in the manufacture of vinegar, though it appears that there 

 would be considerable advantage in such a procedure. The use of 

 pure cultures of yeasts, as is well known, has done very much in 

 improving the quality of beer and preventing losses from the develop- 

 ment of undesirable, so-called wild yeasts 



