Mr. W. K. SuUivau on the nature of Lactic Fermentation. 207 



which the milk underwent in the course of three or four years is 

 not the less interesting in several points of view, and especially 

 as throwing considerable light upon the function of digestion. 



The production of lactic acid from lactine, dui'ing this pecu- 

 liar metamorphosis of caseine in the absence of air, is perhaps a 

 still more important phsenomenon than that metamorphosis itself, 

 inasmuch as it dei'ives peculiar interest from the recent revival of 

 the much-debated question of the nature of fermentation. 



Of the many hypotheses which have been proposed since the 

 time of Stahl, two have especially divided the suffrages of che- 

 mists. According to one, first proposed by Berzelius, vinous 

 fermentation is produced by the kind of action which he de- 

 scribed as catalytic, and which he supposed to be the result of a 

 peculiar force exerted by simple as well as compound bodies, 

 whether in the solid or liquid condition, upon other substances 

 with which they come in contact. The consequence of this 

 action is, that a new arrangement of the molecules of the body 

 acted upon takes place without the elements of the intervening- 

 body necessarily taking any part in the formation of the new 

 substances. According to Faraday, catalytic action does not con- 

 sist in the development of molecular force by mere contact, but 

 rather in an electro-chemical action between the bodies included 

 in the sphere of action. 



Liebig, while adopting the fmidamental idea that molecular 

 motion may be transmitted to a quiescent body, so modified the 

 previous view, that in his hands it became a large generalization, 

 but differing in many respects from the hypothesis of Berzelius. 

 According to Liebig, vinous fermentation may be looked upon as 

 a species of putrefaction of a hydrate of carbon, or rather a meta- 

 morphosis, in which the elements of such a compound molecule 

 arrange themselves under the action of their special affinities into 

 new grou])s. This putrefaction is induced by contact with com- 

 plex azotic bodies in which putrefaction commences spontaneously 

 in the presence of water — non-azotized bodies not being capable 

 of themselves to initiate the change. The azotized bodies which 

 are best adapted to enter into this spontaneous motion of their 

 constituent molecules, are vegetable albumen, gluten, and other 

 similar bodies : putrefying animal matter of all kinds is capable 

 of inducing the same kind of change, but much less perfectly 

 than those named. 



According to this view, Liebig considers yeast to be a sub- 

 stance whose elements exist in a condition of change, the ferment 

 behaving in every respect as an azotic body in a state of putre- 

 faction or decay. Yeast produces fermentation as a result of a 

 progressive decomposition, which it suffers by contact with water 

 and the oxygen of the air. 



