In a paper, entitled “Fermentation in the Leather Industry,”[92] I gave a short account of the progress of putrefaction as it takes place in the animal skin, and also described some of the organisms I had observed in putrefying skin. A small piece of skin was placed in water and allowed to stand at room temperature. During the first two days there was little change, but on the third day a number of swiftly moving darting monads made their appearance. Some of these were propelled by flagellæ, but a few had assumed amœboid forms. A slowly moving bacillus consisting of a long straight rod, apparently broken up into cells exactly like the Vibrio subtilis, illustrated in the “Micrographic Dictionary,” was observed, accompanied by some species of spirillum. Higher organisms present were a Paramœcium and a colourless transparent piece of protoplasm, shaped like a dumb-bell, with a slow rotating motion. On the fifth day the number of vibrios and spirilli had greatly increased, some with a swifter motion than others. There were also many large infusoria present; one of a peculiar double form, which appeared to be a development of the dumb-bell shaped piece of protoplasm seen on the third day. On the seventh day the most striking feature was the great increase in the number of vibrios; the field of the microscope was crowded; masses of the bacilli could be seen clustered round small particles of the disintegrating skin as if feeding upon it; there were more infusoria, many of them short, boat-shaped monads, with a trembling motion, refracting light strongly; these evidently accompany the putrefaction bacteria, and assist in the final disintegration. On the ninth day the piece of skin was entirely dissolved. [92] J.S.C.I., 1894, 218. Procter calls attention to the relative putrescibility of the different constituents of skin, and especially to the rapid putrescence of the lymph and serum. So far as I know, this part of the subject has not been studied at all thoroughly, and there is a considerable field open to workers in our research laboratories. Pure fat is not decomposed by bacteria, but if albuminous matter is present, the fat is split up by several species of bacteria and moulds. Schreiber (73) has shown that the presence of oxygen is necessary. As this subject scarcely comes within the category of putrefaction, I refer you to Schreiber’s paper, and also to an important paper by Otto Rahn (74) recently published.