234 



PHYSIOLOGY OF NUTRITION 



Besides the three bacteria just described other bacteria are 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 of these 

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

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

 (see page 170), possessed keeping qualities, and had the power causing the oxi- 

 dation of alcohol to acetic acid. 



Another special kind of aerobic respiration, similar to that of the acetic acid 

 bacteria just considered, is that of the sorbose bacteria, 2 which merely oxidize 

 sorbite to sorbose. The following equation represents the reaction: 



Sorbite Oxygen Sorbose Water 



2 CeHuOe + 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 



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Fig. 94. — Bacterium aceti, skin 

 formed at the surface of beer. 

 (Highly magnified.) 





Fig. 95. — Bacterium pasteurianum, 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 H 2 0. 



The nutrition of bacteria by mineral substances, which has 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 processes 

 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. 



1 Buchner, Eduard, 'and Guant, Rufus, Ueber die Essiggahrung. Liebig's Ann. Chem. u. Pharm. 349: 

 140-184. 1906. 



2 Bertrand, G., Etude biochimique de la bacterie du sorbose. Ann. chim. et phys. VIII, 3: 181-288. 

 1904. 



