CHEMICAL SCIENCE. 249 



ON THE INFLUENCE OF THE AIR ON FERMENTATION AND 



PUTREFACTION. 



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Fermentation is one of the chemical phenomena whose causes have been 

 the most actively discussed since chemistry became an experimental science. 

 When Gay-Lussac showed that a mixture of sugar and water, with a fer- 

 ment, will remain good in. vacua for an indefinite length of time, and that 

 the reaction commenced on the introduction of a single bubble of oxygen, 

 he attributed the fermentation to electricity. This view was supported by 

 the experiment of M. Collin, according to which, in liquids that do not 

 ferment, the phenomenon of fermentation is instantly produced under the 

 influence of the voltaic current. 



According to Cagnard Latour's theory, yeast is formed of a number of 

 minute vegetable growths, living at the expense of the saccharine matter ; 

 the transformation of this matter into alcohol and carbonic acid, that is, fer- 

 mentation properly so called, is a physiological act, likened to germination, 

 likewise accompanied by the decomposition of the sugar, disengagement 

 of the carbonic acid, and an elevation of temperature. To these theories, 

 exclusively applicable to alcoholic fermentation, and which, with difficulty, 

 explain why a small quantity of yeast is sufficient to decompose a great 

 quantity of sugar, Liebig opposes a purely mechanical theory, which he 

 extends to catalytic effects, as well as to the phenomena of putrefaction, 

 and eremecausis, and which he bases on the principle laid down by La- 

 place and IBerthollet that a molecule, being set in motion by any force 

 whatever, may communicate this movement to another molecule in contact 

 with it ; this principle, which manifests itself whenever the resistance (co- 

 hesion or affinity) is insufficient to be an equilibrium to the movement, 

 moreover accords with the proposition of M. Millon, that, in certain cases, 

 the infinitely large mass submits to the law of the infinitely small quan- 

 tity ; a proposition applied by him to catalytic actions, and justified even 

 by purely physical phenomena. 



Of all the facts adduced against this mechanical theory, doubtless none 

 have been so valuable as those observed by Dr. Ure, Schwann, and Helm- 

 holtz. Accordingly the Gay-Lussac's experiment only succeeds when 

 the oxygen destined to provoke the fermentation has previously passed 

 through a porcelain tube, heated to redness ; blood, muscular flesh, a mix- 

 ture of ferment with sugar and water, may be preserved intact in atmos- 

 pheric air, if kept at aheatof at least 212 Fahrenheit. This led Schwann 

 to think that the spontaneous decomposition called fermentation, or putre- 

 faction, was nothing but the results of the vital manifestations of some 

 cryptogamic or microscopical animalcules, produced by the spores and 

 germs contained in the atmosphere, and becoming developed when they 

 found themselves in a favorable medium. The miasmata and contagions 



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which Liebig considers as connected with the cause to which he attributes 

 fermentation, would, therefore, only proceed themselves from these micro- 

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