The action, therefore, of the acids is a reducing one, inasmuch as skin is dissolved, but as the fibres hold a certain amount of acid, the skin appears to be plumped. Where the acid is a mineral one the skin tans plump, but with a brittle and inelastic fibre, weak organic acids make a plump, soft leather with a moderately elastic fibre, giving to the skin a somewhat india-rubber feel. We thus see that weak acids alone do not produce a similar result to a dung bate, which causes the skin to fall and produces a flat soft leather with a stretch in it, which will not spring back. I have also tried the action of the following Na and NH_{3} salts upon skin:-- _Sodium lactate_, C_{3}H_{5}O_{3}Na, prepared by neutralising 2 grm. lactic acid with sodium carbonate in 1000 c.c. water. The solution was used under the same conditions as the other bating experiments, viz. at 37° C. the reducing action was nil, but on prolonging the digestion, the medium was found to be very suitable for the development of putrefactive organisms, and, as a consequence, the skin was attacked and partly peptonised. _Ammonium lactate_, prepared in a similar way, had an almost identical action on the skin, but was more effective in removing the last traces of lime. _Ammonium butyrate_, prepared as above, removed lime, but instead of a reducing action it appeared to plump the skin slightly. _Action of Bile._ Amongst other compounds in the dung which might have some action on skin were the bile salts and bile colouring matters. (For a full description of these, see Gamgee, Phys. Chem. ii.) Experiments were made with ox bile, 25 c.c. being diluted with 250 c.c. of water. Pieces of sheep grain previously washed in water were digested in this solution at 37° C. for 1–4 hours. The bile had no reducing action on the skin and in fact hardened it, at the same time staining it a dirty yellowish brown, the colour differing from that of the colouring matter of dung (hydrobilirubin). Even after continued standing there was little or no development of bacteria, the bile appearing to have an antiseptic action. _Action of Bacteria._ Having ascertained the action of the chief chemical constituents of the dung, that of the bacteria was next examined. In the first experiment, eliminating all but bacterial action, a tube of nutrient gelatin was inoculated from an active bate. In two days the gelatin had liquefied along the needle track. The culture was now transferred to the following solution:-- Gelatin 4 grm. Dextrose 4 " K_{2}HPO_{4} 1·0 " MgSO_{4} 0·2 " NaCl 0·4 " Water 2000 c.c.