Eitner (Der Gerber, xv., 158) states that a sterile bate is without action on the skins, and appears in that article to attribute the entire working of the bate to the action of micro-organisms. He seems to have based his conclusions on experiments with an old bate sterilised with creolin, which he found had no action on the skins. If, however, a fresh bate be made and boiled for half an hour, then allowed to cool to 90°–95° F., it will be found to have a considerable action on the skins, though not so rapid a one as the unboiled bate. The boiling kills all organisms, and fresh ones have not time to develop from spores still remaining before the experiment is at an end. Lately, the action of unorganised digestive ferments in the dung has been found to be considerable. Thus bating is an exceedingly complex process. The action appears to be threefold:-- (i) A purely chemical action of the soluble salts present in the bate on the lime in the skin.[113] (ii) An action due to organised ferments. (iii) An action due to unorganised ferments. [113] _References to bating_: Procter. Text-book of Tanning, 1885, 184. Der Gerber, x. (1884), 197, Mistbeizen. Der Gerber, xv. (1889), 267. J. Anal, and Appl. Chem., 1893, vii. 87, 95. J.S.C.I., xii. 530, Palmer and Sandford. Salomon, W. J., Tech. Quarter, 1892, v. 81, etc. J.S.C.I., xii. 774, ix. 27. The precise amount of influence each of these actions has on the skin is difficult to assign. The chemical action of the ammonia compounds dissolves the lime remaining in the skin, but the simple removal of the lime is not sufficient, as may be shown by removing it completely with dilute hydrochloric acid or other similar means, and washing perfectly free from acid in distilled water. When tanned, such a skin is hard and brittle. The organised ferments or bacteria, of which there are many species in the bate, probably act on the skin by secreting soluble ferments, which have the power of dissolving hide fibre. I have isolated in plate cultivations several species which liquefy the gelatin. If skins are allowed to lie in the bate, zoogloæ of these bacteria collect in the folds and attack the fine “grain,” so that the leather is covered with lines and markings, or “flaked.” Thus the operation is a very critical one, requiring careful watching; under certain atmospheric conditions and at a temperature of 35°–40° C. the skin, if only left a short time too long, will completely melt away. The more skin substance is dissolved in the liquid, the more rapid and pronounced the bacterial action becomes.