1 6 THEORIES OF FERMENTATION 



The ocular demonstration, in individual instances, of the untenable nature 

 of the hypotheses supporting this theory, to those whom the representations 

 of Latour, Kutzing, and Schwann had not succeeded in convincing, was the 

 congenial task undertaken by Pasteur, and brought by him to a successful 

 issue with great experimental skill. 



16. Pasteur's Theory of Fermentation (III.). 



The victorious antagonist of the theory of spontaneous generation was not 

 content with controverting the views of Liebig ; he also sought to erect a better 

 theory in its stead. According to this doctrine, it is the lack of free oxygen that 

 leads to the fermentation being set up by the organism as a means of supplying 

 itself with the energy it requires by seizing upon the oxygen thereby obtain- 

 able. " Fermentation is life without air." A very slight experience in this 

 matter suffices for the recognition of the fact that this theory takes no account 

 of the several kinds of fermentation in which the presence of oxygen is a neces- 

 sary condition, viz., the so-called oxidation fermentations the best example of 

 which is afforded by the acetic fermentation. In this respect the theory cannot 

 be further alluded to in the present chapter, which is devoted to general con- 

 siderations. It will be fully dealt with in a subsequent chapter. The only 

 remark to be made now is that this theory also has proved untenable. 



The permanent value of the services rendered to Fermentation Physiology 

 by Pasteur are not diminished by the disproval of his theory of fermentation, 

 since they have their root in the successful endeavour, by means of careful and 

 extensive experimental demonstration, to bring into universal recognition the 

 theory originated but only imperfectly formulated by Cagniard, Kutzing, and 

 Schwann, of the causative connection between fermentation and the vital 

 activity of the microbe. 



17. C. Nag-eli's Physico-Molecular Theory. 



Although it was by this time indubitably established that without the vital 

 activity of micro-organisms no fermentation could occur, no clear account had 

 been given as to how the activity itself was exerted. Several explanations 

 were possible. According to one which was especially advocated by Kutzing and 

 Pasteur, a decomposition was effected within the cells of the organic ferments, 

 which obtained their nourishment from the fermenting material (e.g. sugar) and 

 discharged the fermentation products as waste matter. 



According to another, the decomposing force simply emanated from the cells 

 and became the direct cause of the decomposition of the fermentable matter 

 around them. 



The physico molecular theory, proposed by NAGELI (II.), expresses this view 

 in the following words : " Fermentation is, therefore, the transference of con- 

 ditions of movement in the molecules, atomic groups, and atoms of the various 

 compounds constituting the living plasma (which compounds remain chemically 

 unchanged) to the fermentative material, whereby the equilibrium of its molecules 

 is destroyed and their dissociation induced." The radius of the sphere of influence 

 of the individual yeast cells is estimated by Nageli as from 20 to 50 /*. 



This definition differs from that formerly given by Liebig merely in a single, 

 though important, consideration, viz., it regards the living cell as the source of 

 action, whereas the other definition speaks of inanimate albuminoid substances. 

 .Nageli was, however, unable to prove the correctness of his theory, and the calcula- 

 tions deduced from other observations which he brought forward in support 

 thereof have in course of time proved inapplicable. 



