ALCOHOLIC FERMENTATION 377 



ductivity of an albumen solution which was being hydrolysed 

 by pepsin.* 



Sorensen f found that he could obtain a measure of the 

 amount of protein hydrolysed, by determining the number of 

 free carboxyl groups in the mixture. By adding an excess of 

 formalin, the free amino groups were neutralized ; the car- 

 boxyl groups were then estimated by adding an excess of N/5 

 baryta solution and titrating back the excess by means of 

 hydrochloric acid. 



ZYMASE AND ALCOHOLIC FERMENTATION. 



The formation of alcohol from fluids containing sugar has 

 been known and practised for thousands of years, and the use 

 of yeast in the manufacture of alcoholic beverages and of bread 

 is an ancient industry. As is well known, when yeast is placed 

 in a sugar solution, fermentation begins sooner or later, the 

 principal end products being alcohol and carbon dioxide; 

 substances other than ethyl alcohol, however, are formed, 

 especially glycerol, succinic acid and amyl alcohol,! the last 

 more particularly in the fermentation of the sugars obtained 

 from wheat and potato starch. Alcoholic fermentation is due 

 to the activity of the enzyme zymase, which was first separated 

 from the yeast cell by Buchner, whose work|| marks the 

 beginning of an epoch of vigorous investigations into this and 

 kindred subjects. 



*Cf. Bayliss: "Arch. Sciences Biol.," St. Petersburg, 1904, II (supplem.). 



f Sorensen : Biochem. Zeit.," 1908, 7, 45. 



+ Amyl alcohol, using the term in its general acceptance, is a mixture of 



CH \ 

 two isomeric primary alcohols, isobutyl carbinol J)CH . CH 2 . CH 2 OH and 



CH 3 



secondary butyl carbinol CH 3 CH 2 CH CH 2 OH. The two substances to- 

 gether form " fusel oil," which is the harmful constituent of cheap spirit made 

 from potatoes 



They appear to be produced from leucine (CH 3 ) 2 CH CH 2 CHNH 2 COOH, 

 CH 3 



and isoleucine CH 3 CH 2 CH CHNH 2 COOH, which are constituents of the 

 protein molecule, by loss of CO 2 and replacement of the NH 2 group by OH 

 (see p. 343). The mixture is optically active owing to the asymmetric carbon 

 atom of the secondary butyl carbinol. 



For an account of our knowledge of alcoholic fermentation prior to 1897, 

 see Green : " Nature," 21 April, 1898. 



II Buchner : " Ber. deut. chem. Gesells.," 1897,30, 117, mo; 1898, 31, 568; 

 Buchner and Rapp : id., 1897, 30, 2668 ; 1898, 31, 209, 1084, 1090 ; 1899, 32, 127, 



