FERMENTATION AM) RKSl'I RA ! I < >\ 



2 3 I 



Besides the three bacteria just described other bacteria arc also employed in 

 the manufacture of vinegar. Bacterium xylinum is commonly used in England. 



The oxidation of alcohol to acetic acid is carried on in the cells <>i 

 bacteria by a specific intracellular enzyme. Büchner and Gaunt 1 obtained 

 acetone preparations of acetic acid bacteria, which, like Buchner's "zymin" 

 (see page 167), possessed keeping qualities, and had the power < ausing the oxi 

 dation of alcohol to acetic acid. 



Another special kind of aerobic respiration, similar to thai <>1" the aceti< a« id 

 bacteria just considered, is that of the sorbose bacteria,- which merely oxidize 

 sorbite to sorbose. The following equation represents the reaction: 



Sorbite Oxygen Sorbose Water 



2 C fi H 14 6 + 2 = 2 C 6 H 12 6 + 2 H 2 0. 

 Still other alcohols are oxidized by microorganisms, producing the correspond- 

 ing aldehydes and ketones. Such a physiological oxidation process furnishes 



Fig. 94. — Bacterium aceti, skin 

 formed at the surface of beer. 

 (Highly magnified.) 



Fig. 95. — Bacterium pasleurianum, cells 

 from skin formed at the surface of beer. 

 (Highly magnified.) 



the best method for obtaining dihydroxyacetone from glycerine, the reaction 

 being as represented below. 



Glycerine Oxygen Dihydroxyacetone Water 



2 CH 2 OH-CHOH-CH 2 OH + 2 = 2 CH 2 OH-CO-CH 2 OH + 2 HoO. 



The nutrition of bacteria by mineral substances, which lias been previously 

 considered (see page 47), also really represents special cases of aerobic respira- 

 tion. One form of bacteria oxidizes hydrogen sulphide, another oxidizes am- 

 monia, a third oxidizes hydrogen, etc. The cosmic importance of these special 

 types of physiological oxidation is very great, for it is through these pro« ess« - 

 that the natural circulation of sulphur, nitrogen, and hydrogen is largely brought 

 about. The total amounts of the various chemical elements available for life- 

 processes upon our planet remain practically constant, but the various com- 

 pounds are always decomposing and being reformed, so that the elements are 

 forever in a state of circulation, and bacteria play a very important role in this 

 great process. 



'Buchner, Eduard, and Gaunt, Rufus, Ueber die Essiggahrung. Liebig'a Ann. Chem. u. Pharm. 

 349: 140-184. [906. 



■ Bertrand, G., Etude biochimique de 



1904- 







