Nencki explains, for example, the metamorphosis of leucin by putrefaction in this way: The bacteria decompose the water into hydrogen and hydroxyl, which act upon the leucin as follows:-- CH_{3} \ OH CH - CH_{2} - CH - COOH + H = NH_{3} / | CH_{3} | Leucin NH_{2} + OH - CH_{2} (CH_{2})_{4} COOH (oxycaproic acid) The resulting oxycaproic acid is then split up by the second water molecule into methylenglycol and valerianic acid:-- OH | CH_{2} OH | + H = CH_{2} (OH)_{2} + CH_{3} (CH_{2})_{3} COOH (CH_{2})_{4} | COOH The methylenglycol, which changes into formaldehyde and water, is now split up into CO_{2} and hydrogen, as it would be by melting with caustic alkali. OH H H.OH / C O + = CO + 2H_{2} H H.OH \ OH As we shall see in the chapter on the action of enzymes, the phenomena are of a catalytic nature. Any urea present is decomposed, by the direct action of micrococcus ureæ, into ammonium carbonate and ammonium carbamate, so that it does not play any part in the bating process as usually carried out with dung which has been kept for some time, but the ammonia produced plays an important part in the chemical action of the bate, as we have already seen. If, however, dung containing the urinary products be used in a fresh condition, the urea has indirectly a very important influence on the bating, as it favours the permeability of the skin fibre. (See p. 72.) The fermentation of the cellulose in the dung has not been studied from the bating standpoint, but it is well known that it is fermented by various species of bacteria, which have been grouped together under the generic name of Amylobacter. Deherain and Gayon first showed that the solution and fermentation of cellulose in the form of dead vegetable matter, which had previously been observed, also took place in dung. Van Tieghem, in 1879, showed that the solution of cellulose is caused by bacteria, whose properties correspond with those described by him as Amylobacter. Tappeiner was able to ferment cellulose by mixed cultures of bacteria from the intestines of oxen--in neutral solution, CO_{2}, methane, H_{2}S, aldehyde, butyric acid, and acetic acid, were all recognized. In alkaline solutions, the principal products were CO_{2} and hydrogen, together with the same by-products as before.