264 POISONS, CONTAGIONS, MIASMS. 



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 dif- 

 ferent 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, or into 

 butyric acid. 



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

 sugar gradually disappears, but that, when added to vegetable 

 juices which contain gluten as well as sugar, it is reproduced 

 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 still 

 remaining in the liquid does not suffer change from contact with 

 the newly-deposited yeast, but retains all the characters of 

 gluten. 



Yeast is a product of the decomposition of gluten ; but it 

 readily passes into c, second stage of decomposition when in con- 

 tact with water. On account of its being in this state of further 

 change, yeast excites fermentation in a fresh solution of sugar ; 

 and if this second saccharine fluid should contain gluten (should 

 it be wort, for example), yeast is again generated, in consequence 

 of the transposition of the elements of the sugar exciting a 

 similar change in this gluten. 



