50 BIOLOGY AND TECHNIQUE 



Lactase. — Lactose-splitting ferments are extremely common both 

 among bacteria and among the yeasts. The process is here again a 

 hydrolytic cleavage resulting in the formation of the monosaccharids 

 as dextrose and galactose. 



Maltase. — ^A maltose-splitting ferment has also been found in the 

 cultures of many bacteria, leading to the formation of dextrose. 



Lactic Acid Fermentation. — Lactic acid (oxyproprionic acid, CjHg O3) 

 is one of the most common substances to appear among the prod- 

 ucts of bacterial activity, both in media containing carbohydrates 

 and in those consisting entirely of albuminous substances. In most of 

 these cases, the lactic acid is formed merely as a by-product accom- 

 panying many other more complicated chemical cleavages. In some 

 instances, however, lactic acid is produced from carbohydrates, both 

 disaccharids and monosaccharids, as an almost pure product due to a 

 specific bio-chemical process. The reactions taking place in this phenom- 

 enon may be briefly expressed according to the following formulae: 



C,2 H,, 0„ + H, = 4C3 He O3 

 Lactose Lactic acid 



or 



Ce H12 Oj = 2C3 H„ O3 

 Dextrose Lactic acid 



In the same way lactic acid may be produced by bacteria from levu- 

 lose. 



Examples of lactic acid formation are furnished by the streptococcus 

 lacticus, and B. lactis aerogenes. In the case of the former, the fer- 

 mentation may indeed proceed by the simple chemical process indi- 

 cated in the formulae, since the action of the bacillus is entirely unac- 

 companied by the evolution of gas. 



Numerous other bacteria produce large amounts of lactic acid from 

 lactose, possibly by chemical processes less simply formulated. Among 

 these are bacilli of the colon group, B. prodigiosus, B. proteus vulgaris, 

 and many others. Although lactic acid is usually the chief product in 

 the bacterial fermentation of the simpler carbohydrates, acetic, formic, 

 and butyric acids may often be found as by-products in variable 

 amounts.' 



Oxydases (Oxydizing Enzymes). — ^The most common example of 

 oxidation by means of bacterial ferments is the production of acetic acid 



> Buchner und Meisenheimer, Ber. d Deut. chem. Gesellsch., xxxvi, 1903. 



