1 8 THEORIES OF FERMENTATION 



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

 sidered it as being so self-evident to chemists as not to require any demonstra- 

 tive 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, merit special mention in this place, because they 

 brought our ideas into closer harmony with the ferment theory, at least so far as 

 regards the ammoniacal fermentation of urine. Moreover, they have greatly 

 strengthened the position of the ferment theorists by proving that this urase 

 cannot be placed amongst inorganic chemical substances, in the ordinary sense of 

 the term, but is really an intermediate stage between these and living pi^otoplasm. 

 Miquel goes so far as to say that his urase is actually protoplasm, chiefly differing 

 from that of the cell contents in that it dispenses with the protection of the cell 

 wall, and remains and works on the outside. 



The reader desiring fuller information on the properties of the enzymes than 

 can be obtained from the present work is referred to the comprehensive treatise 

 published by E. BOURQUELOT (I.) in 1896. 



19. General Definition of Fermentation. 



We will now pass in review all the preceding explanations, and attempt to 

 extract from each of them whatever can possibly afford us assistance in finally 

 arriving at a satisfactory definition of the term fermentation. In the first place, 

 Liebig's explanation certainly does not call for further consideration in this con- 

 nection. In the results of the remaining researches we find one factor common 

 to all, and that is the certainty that, for the inception and continuance of the 

 process, which in harmony with the limitation expressed in i we have 

 hitherto entitled " fermentation," the presence and active collaboration of low 

 types of living organisms is a prime essential. Concerning the nature of the 

 influence, whether direct or indirect, of these organisms, opinions are, however, 

 divided. 



If, now, the instigators of fermentation be examined seriatim according to 

 the method outlined later on, it will be found that not only are they vegetable, 

 but also that all belong to the same class, and that, too, the lowest in the vegetable 

 kingdom, namely, the fungi. The power of inciting fermentation is, however, 

 restricted to comparatively few of the genera of this class. Nevertheless, these 

 latter are so intimately connected with the others, from a botanico- morphological 

 point of view, that it is impossible- to classify the fungi into two sub-groups, 

 characterised by the presence or absence of this faculty, without introducing 

 serious systematic anomalies. 



The limitation that can be given to the definition of fermentation may be 

 thus expressed : " Fermentation is a decomposition effected by the vital activity 

 of fungi." Nevertheless, as is evident from what has already been intimated, 

 no greater precision can at present be imparted to such part of this definition as 

 refers to the nature or mode of action of the ferment. On the other hand, as 

 will soon be apparent, the word " decomposition " must give place to a term 

 that is both more accurate and more comprehensive. 



The phenomena of fermentation forming the starting-point from which the 

 workers from Cagniard to Nageli began their researches, and which up to the 

 present have been the sole subject under our consideration, possess one charac- 

 teristic in common, i.e. they are always attended by the degradation of complex 

 organic compounds into simpler ones. By regarding this characteristic by itself, 



