180 FERMENTATION. [ VII. 



Mitscherlich's experiments lead to a similar conclusion. 

 (Berzelius Jahresb. 1846.) The fermentable substances were 

 put into flasks witli water, and boiled to destroy the vitality 

 of seed. One flask was left open, and the other closed with 

 filtering paper, pasted tightly around the edges. The open 

 flask soon, showed signs of fermentation in the formation of 

 mould ; while the other did not exhibit any such change in the 

 course of months, the paper apparently filtering ofi" the germs 

 from the air which entered the vessel. 



Doppning and Struve, repeating Helmholz's experiments, 

 drew the conclusion that all nitrogenous substances undergo 

 decomposition, even in air previously ignited, and that it is 

 chiefly prevented or diminished by a boiling temperature. 

 They also observed that paper, straw, and other porous bodies 

 may be fermented without the presence of a ferment, but 

 that the resulting product is butyric acid and not alcohol. 

 The same fermentation occurs when solutions of sugar are 

 brought in contact with powdered charcoal or sulphur, but 

 in the latter case, a little tartrate of ammonia should be added. 

 (Bullet, de St. Petersbourg, 1847.) 



Action of Ferment on Sugar. — Dubrunfault's examination 

 of the changes sufl'ered by cane-sugar, in the fermenting pro- 

 cess, previous to the formation of alcohol and carbonic acid, 

 led him to the following conclusions. The altered cane-sugar 

 (or its analogous grape-sugar or fruit-syrup) is not a simple 

 variety of sugar ; only a certain quantity of it becomes glu- 

 cose by crystallization, the residue polarizing to the left with 

 the same power that the separated grape-sugar polarizes to 

 the right. In the vinous fermentation of the altered sugar, 

 that which disappears in the first part of the process is op- 

 tically neutral, while the sugar which disappears last polarizes 

 strongly to the left. No one sugar is exclusively decomposed 

 before another in fermenting mixed sugars. The sugar pro- 

 duced from starch, by the action of malt, is not identical with 

 grape-sugar ; for the former is less soluble in alcohol, less 

 liable to change by ebullition, or the alkalies, and its polarizing 

 power is three times that of the latter. The optical deflecting 



