1258. The changes which organic matters undergo in decomposing have been arranged under four heads, viz. fermentation, putrefaction, decay, and mouldering, which are thus explained by Professor Solly: - 'The complicated changes which organic matters undergo in decomposing are generally divided into four separate classes, namely, fermentation, or the formation of new compound substances, by the partial decomposition of a compound, the change being induced or commenced in consequence of the presence of some other decomposing matter. Putrefaction, or the complete decomposition of organic matter and its conversion into different inorganic compounds, such as water, ammonia, carbonic acid, sulphuretted hydrogen, &c. Decay, a slow process of oxidation, almost analogous to combustion, differing from putrefaction in being dependent on the presence of free oxygen or air. This change is always accompanied by the evolution of heat: mouldering, a change intermediate between putrefaction and decay, taking place in organic matters exposed to the action of water, but not to that of air.' (Solly's Rural Chemistry, 2nd edit., p. 171.)
