132 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



flask ; on heating the latter on the water-bath alcohol will 

 be seen first of all to condense in the tube, and afterwards to 

 pass off as vapour, which can be easily detected by applying 

 a light, when the characteristic non-luminous flame of alcohol 

 is produced. This is the alcoholic fermentation of sugar which 

 is the foundation of the great brewing and distilling industries. 

 As it is of great technical and, one might add, social importance, 

 it has been studied from the very earliest times, and only 

 recently great additions have been made to our knowledge of 

 it. The history of the subject is very largely the history of 

 fermentation, and some brief account of the older theories 

 of this process will not only be of interest in itself, but may 

 enable the full bearing of modern investigations to be better 

 understood. 



Alcoholic fermentation has been known from the very 

 earliest times ; the preparation of beer from barley, of wine 

 from grapes and the leavening of dough are mentioned in the 

 oldest known writings. By the alchemists alcoholic fermenta- 

 tion was much studied ; the Philosopher's Stone was considered 

 to be a kind of ferment. No very clear ideas were, however, 

 possessed by the alchemists in regard to what took place, and 

 a confusion existed in their time between fermentation and 

 effervescence, which were not properly distinguished till the 

 middle of the seventeenth century. 



The great medical chemist Libavius (1595) considered that 

 fermentation was a process akin to digestion, a guess the true 

 bearing of which it is hardly likely that its author properly 

 appreciated. 



An even more happy suggestion was made in 1648 by Van 

 Helmont, who stated that out of the ferment something passes 

 into the fermenting liquid, which grows in it as a seed. 



The authors of the phlogistic theory of combustion, Becher 

 and Stahl, paid attention to alcoholic fermentation. Becher 

 showed that the juice of grapes does not ferment if the skin of 

 the grape is unruptured, and thus showed that alcohol was not 



