724 PRELIMINARY OBSERVATIONS. 



in a state of decomposition at the time. The yeast is only 

 active when, by access of air, it has become subject to oxidation, 

 and the decomposition of the sugar is looked upon by M. Liebig 

 as a reflex action of the decomposition of the yeast. The views 

 of that eminent philosopher on the action of yeast and other 

 ferments will be best explained in his own words. 



" This action may be expressed by the following law, long 

 since proposed by Laplace and Berth ollet, although its truth 

 with respect to chemical phenomena has only lately been 

 proved. ( A molecule set in motion by any power can impart 

 its own motion to another molecule with which it may be in 

 contact/ " 



This is a law of dynamics, the operation of which is manifest 

 in all cases, in which the resistance (force, affinity, or cohesion,) 

 opposed to the motion is not sufficient to overcome it. 



We have seen that ferment or yeast is a body in the state of 

 decomposition, the atoms of which, consequently, are in a 

 state of motion or transposition. Yeast placed in contact with 

 sugar, communicates to the elements of that compound the 

 same state, in consequence of which, the constituents of the 

 sugar arrange themselves into new and simpler forms, namely, 

 into alcohol and carbonic acid. In these new compounds the 

 elements are united together by stronger affinities than they 

 were in the sugar, and therefore under the conditions in which 

 they were produced further decomposition is arrested. 



We know, also, that the elements of sugar assume totally 

 different arrangements, when the substances which excite their 

 transposition are in a different state of decomposition from the 

 yeast just mentioned. Thus, when sugar is acted on by rennet 

 or putrefying vegetable juices, it is not converted into alcohol 

 and carbonic acid, but into lactic acid, mannite, and gum. 



Again, it has been shown, that yeast added to a solution of 

 pure sugar gradually disappears, but that when added to ve- 

 getable juices which contain gluten as well as sugar, it is re- 

 produced by the decomposition of the former substance. 



The yeast with which these liquids are made to ferment, has 

 itself been originally produced from gluten. 



The conversion of gluten into yeast in these vegetable juices 

 is dependent on the decomposition (fermentation) of sugar; for, 

 when the sugar has completely disappeared, any gluten which 



