The earlier products of putrefaction are very similar. Many bacteria have the power of liquefying gelatin-jelly. This has been shown by Brunton and McFadyen[37] to be due not to the direct action of the bacteria, but to a soluble zymase secreted by them which peptonises the gelatin. Its action is favoured by an alkaline condition, and destroyed by a temperature of 100° C.[38] As putrefaction progresses, the solution becomes very acid from the formation of butyric acid, and later on ammonia and amido-acids are formed. [37] R. S. Proc., xlvi. pp. 542-53. [38] Compare pp. 17, 171; also Ch. Zeit., 1895, p. 1487. Fahrion,[39] starting with the idea that albuminoids and gelatin were condensation products of a lactone character (L.I.L.B. p. 185), and that they might, like lactones, be depolymerised by saponification, digested these bodies with alcoholic soda till they were dissolved, and on neutralising the solution with hydrochloric acid, of which the excess was driven off by repeated evaporation, and removing the sodium chloride by treatment with alcohol, obtained in each case bodies of acid reaction, which from their composition he supposed to be identical with Schützenberger’s proteic acid, C₈H₁₄N₂O₄, which is soluble in water and alcohol, insoluble in ether and petroleum, uncrystallisable, and forming uncrystallisable salts. Fahrion suggested that the nitrogenous character which Eitner attributed to his “dégras-former” (p. 370) was probably due to contamination by this body; and that its formation might be utilised in the analysis of leather and other proteid bodies. These products have since been further investigated by Prof. Paal and Dr. Schilling,[40] who show that they contain hydrochloric acid, to which their acid reaction is due, and that they are identical with the peptone salts previously obtained by Prof. Paal (v. s.) by digestion of proteids with hydrochloric acid. The free peptones are strongly basic. [39] Ch. Zeit., 1895, p. 1000. [40] Ch. Zeit., 1895, p. 1487. By dry distillation of gelatin a mixture of pyrrol and pyridin bases are produced. This is commercially obtained by the distillation of bones, and is known as “bone oil,” or “Dippel’s animal oil.” Pyrrol, C₄H₅N, resembles phloroglucol in giving a purple-red colour to fir wood moistened with hydrochloric acid (p. 299).