16 THKORIKS OF FKRM KNTATION 



The ocular demon in individual instances, of the untenable nature 



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

 of Latour, Kiitzing, and Bohwann had not succeeded in convincing, was the 

 congenial ta-^k 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 wit LOg t he \ ieWB of Liehig ; he also sought to erect a better 



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

 le.ids to the fermentation being set up by the organism a- a means of supplying 

 itself with the enei -ei/ing upon the oxygen thereby obtain- 



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

 matter MI:' he recognition of the fact that this theory takes no account 



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

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

 whi'-h i> atlbrded by the acetic fermentation. In this respect the theory cannot 

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

 It \\ill lie 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 n iginated but only imperfectly formulated by Cagniard, Kiitzing, and 

 Schuann, of the causative connection between fermentation and the vital 

 activity of the microbe. 



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



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

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

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

 irere po il.le. According to one which was especially advocated by Kiitzing and 

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

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

 di>i barged the fermentation products as waste matter. 



ther, the decomposing force simply emanated from the cells 

 '(came the direct cause of the decomposition of the fermentable matter 

 .I till-in. 



The pliNsiro molecular theory, proposed by K \.i:u (II.), expresses this view 

 in the following words: u l-Vrmentation is, t herefore, the transference of con- 

 dition.^ of movement in the molecules, atomic groups, and atoms of the various 

 compo -tit ut ing tin- living plasma (which compounds remain chemically 



mged) to tin- Fermentative material, whereby the equilibrium of its molecules 

 is destroyed and their di>.->ciat ion induced." The radius of the sphere of influence 

 iual yeast cells is estimated by Niigeli M from 20 to 50 /*. 



M di!lei> from that formerly given by Lichig meivly in a single, 

 h important, consideration, vi/.., it regards the living cell as the source of 

 whcica> the other definition >p-ak> of inanimate albuminoid substances. 

 Nageli was, however, unable to prove the c<> of his theory. ami the calcula- 



tions deduced from other observations which he brought forward in support 

 me of time proved inapplicable. 



