22 THEORIES OF FERMENTATION. 



pepsin, subsequently also named peptase, which in faintly acid 

 solutions resolved undiffusible albumen into assimilable dissociation 

 products. Since that time the same enzyme has also been detected 

 in various vegetable organisms, many varieties of bacteria in par- 

 ticular having the power of elaborating it. There will be ample 

 opportunity for reference to this point along with the other known 

 enzymes at a subsequent stage. At present we have only to 

 consider them as the basis of a theory of fermentation, the formu- 

 lation of which dates back as far as 1858, but has come to the 

 front more of late years and so far as can be judged from the 

 data at present available will acquire still greater importance. 



As we have observed in 10, the meaning attached, under the 

 influence of alchemical views, to the word ferment was, until the 

 close of the eighteenth century, very comprehensive, and it was 

 only then that the restriction of the term to bodies inciting 

 fermentation began. Contemporaneous with the development 

 of positive knowledge with regard to these bodies was the dis- 

 covery of the enzymes, the behaviour of which resembled that of 

 the former, in so far that they exhibited a capacity of inducing 

 decomposition. Moreover, the obscurity in which these organisms 

 were still enshrouded was equally mysterious in both cases ; and, 

 since the organic nature of the true instigators of fermentation 

 was either unknown or was not considered worth attention by the 

 chemists of the day, it happened that the name "ferment" was 

 also applied to the newly discovered enzymes. With an increas- 

 ing insight into the true state of the matter grew the conviction 

 that two very different things had been grouped under one name, 

 and this conviction found expression in the distinction thence- 

 forward of the true instigators of fermentation as organised or 

 structural ferments, whilst the enzymes were designated un- 

 organised or structureless ferments. These terms are still 

 current in chemical text-books, whereas in Fermentation Physio- 

 logy it is customary to speak merely of fermentative organisms 

 on the one hand and of enzymes on the other. 



M. TRAUBE (I. and II.) in 1858 made the origin and influence 

 of these enzymes the basis of a new conception (Ferment Theory) 

 of fermentation, according to which this process is not instigated 

 by the organisms themselves, but by the enzymes formed as pro- 

 ducts of their vitality and excreted by them. 



This theory was accepted by many persons, e.g. by Hoppe- 

 Seyler, who considered it as being so self-evident to chemists as 

 not to require any demonstrative evidence. Nageli, on the other 

 hand, advocated its rejection, mainly for the reason that he was 

 not convinced as to the existence of any fermentative enzymes. 

 Numerous workers have, however, since investigated this point, 

 with the result that Traube's opinion has again found general 

 acceptance. The investigations of Miquel with regard to urase, 

 i.e. the enzyme excreted by the bacteria of uric fermentation, 



