II. 



THEORIES OF FERMENTATION. 



10. Stahl's Theory of Fermentation. 



WHOEVER was the first to leave the juice of sweet fruit to itself in storage for 

 a few days had the pleasure of observing a phenomenon hitherto unknown 

 the incipient decomposition of the mass which we nowadays term alcoholic 

 fermentation. This observation was made at so early a date that we have no 

 record of it beyond myth and tradition. The Greeks feted the deity Bacchus 

 as the inventor of wine, and the Egyptians ascribed to Osiris the first introduc- 

 tion of brewing. 



Acquaintance with the nature of this phenomenon was, however, of an 

 extremely superficial character for a very long time. Even in the later Middle 

 Ages the word fermentatio (fermentation) was employed as synonymous with 

 digestio (digestion), the latter word being also currently used to denote any form 

 of chemical reaction ; and the word " ferment " was applied to any body capable 

 of producing such reaction. 



At an early date it would necessarily be noticed that the " must " when in a 

 state of fermentation became covered with a froth, and that at the end of this 

 operation a copious deposit, viz., yeast, was left at the bottom of the vessels. 

 Fermentation was therefore looked upon as a process of purification, by which 

 the initially turbid and discoloured liquid was so improved and freed from dirt, 

 that the purified alcohol exhibited its true properties. For this reason the 

 deposit was described as the faeces vini or faeces cerevisice, i.e. the excrement of 

 the wine or beer. This view was held by, e.g. Basilius Valentinus, a German 

 monk and alchemist, who lived at Erfurt early in the fifteenth century. 



It was also noticed that this sediment was a powerful ferment, i.e. it was 

 capable of rapidly exciting a brisk fermentation in still unfermented liquids, 

 such as wine-must or beer-wort. This idea was adopted in other branches of 

 chemistry, so that any reaction was considered as elucidated when the body 

 acting as " ferment " therein could be identified. Moreover, the " philosopher's 

 stone," the goal of the labours and aspirations of the alchemists, was nothing 

 but the much sought for, but never discovered, universal " ferment " for every 

 possible chemical process ! 



Among the disciples of the alchemic school, one other, viz., STAHL (I.), 

 deserves mention, because his views on the nature of fermentation were adopted 

 by Liebig a hundred and forty years later. Stahl extended the definition of 

 fermentation to all forms of decomposition, his theory being expressed verbatim 

 as follows : " Putrefaction (and also fermentation) is internal movement. A 

 body undergoing such internal movement may easily induce the same in any 

 other body, which, though still quiescent, is susceptible of such movement." 



11. Gay-Lussac's Opinion. 



Stahl's view remained in vogue until the commencement of the nine- 

 teenth century, when Gay-Lussac, in 1810, enunciated a new theory to a new 



