294 YEAST OR FERMENT. 



gen of that substance as well as that of the water, in order to form 

 carbonic acid ; and the sulphur and hydrogen being set free will 

 combine whilst in the nascent state, producing hydrosulphuria 

 acid, which will be again decomposed if metallic oxides be 

 present ; and the results of this second decomposition will be 

 water and metallic sulphurets. 



The putrefied leaves of woad (Insatis tinctoria), in contact with 

 indigo-blue, water, and alkalies, suffer further decomposition, and 

 the indigo is deoxidized and dissolved. 



The mannite formed by the putrefaction of the juice of the beet- 

 root and other plants containing sugar, contains the same number 

 of equivalents of carbon and hydrogen as the sugar of grapes, but 

 two atoms less of oxygen ; and it is highly probable that it is pro- 

 duced from sugar of grapes, contained in those plants, in precisely 

 the same manner as indigo-blue is converted into deoxidized 

 white indigo. 



During the putrefaction of gluten, carbonic acid and pure hy- 

 drogen gases are evolved ; phosphate, acetate, caseate, and lactate 

 of ammonia being at the same time produced in such quantity, 

 that the further decomposition of the gluten ceases. But when 

 the supply of water is renewed, the decomposition begins again, 

 and in addition to the salts just mentioned, carbonate of ammonia 

 and a white crystalline micaceous matter (caseous oxide) are 

 formed, together with hydrosulphate of ammonia, and a mucila- 

 ginous substance coagulable by chlorine. Lactic acid is almost 

 always produced by the putrefaction of organic bodies. 



We may now compare fermentation and putrefaction with the 

 decomposition which organic compounds suffer under the influence 

 of a high temperature. Dry distillation would appear to be a 

 process of combustion or oxidation going on in the interior of a 

 substance, in which a part of the carbon unites with all or part 

 of the oxygen of the compound, while other new compounds con- 

 taining a large proportion of hydrogen are necessarily produced. 

 Fermentation may be considered as a process of combustion or 

 oxidation of a similar kind, taking place in a liquid between the 

 elements of the same matter, at very slightly elevated temperature ; 

 and putrefaction as a process of oxidation, in which the oxygen 

 of all the substances present comes into play. 



