ALCOHOLIC FERMENTATION 365 



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,f whose work | marks the 

 beginning of an epoch of vigorous investigations into this and 

 kindred subjects. 



It must, however, be remembered that many other enzymes 

 besides zymase exist in Saccharomyces ; e.g., diastase, invertase, 

 trypsin and emulsin. 



For laboratory purposes the fermentative activity of Sac- 

 charomyces may be quickly and conveniently illustrated by 

 the use of Pasteur's solution, the composition of which is as 

 follows : — 



Ammonium tartrate, 50 grams 

 Potassium phosphate, 10 grams 

 Calcium phosphate, i g»am 

 Magnesium sulphate, i gram 



These salts are thoroughly ground and mixed in a mortar, and 

 I gram of the mixture together with 12 grams of glucose are 

 dissolved in 70 c.c. of water, the yeast being added to the 

 solution. 



If cane sugar be used, marked fermentation will only 

 begin after an interval of time has elapsed, during which the 



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



CHgX 



two isomeric primary alcohols, isobutyl carbinol /CH . CHo . CHjOH and 



CH, 



I 

 secondary butyl carbinol CH, — CHj — CH — CHgOH. 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 (CH3)2CH— CH,,— CHNH„COOH, 

 CH3 



I 

 and isoleucine CH3CH2— CH— CHNHjCOOH, which are constituents of the 

 protein molecule, by loss of C0„ and replacement of the NH, group by OH 

 (see p. 329). The mixture is optically active owing to the asymmetric carbon 

 atom of the secondary butyl carbinol. 



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

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



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

 Bughner and Rapp : id,, 1897, 30, 2668 ; 1898, 31, 209, 1084, logo •, 1899, 32, 127. 



