The different effects of old and new limes are too well known to practical tanners to be discounted by laboratory experiments, even if they were not confirmed not only by Eitner’s results, but by a considerable amount of work done in the Author’s laboratory and elsewhere; while the necessity of bacterial action is at least rendered probable by the fact that soda solutions, which are completely sterile to bacteria, fail to unhair hides which have not previously undergone some putrefaction (see p. 137). In some experiments undertaken at the suggestion of the Author it was found that a perfectly fresh and sterilised calf-skin which was not unhaired after ten days’ liming in sterilised lime-liquor unhaired rapidly on the addition of a bacterial culture to the lime. It is extremely difficult to exclude bacteria, and even where perfectly fresh skins treated with chloroform or carbon disulphide were employed, bacteria were always to be recognised when the skin was ready for unhairing. Von Schroeder’s work, is, however, so painstaking and reliable, that these divergent results must be explained as other than experimental errors. With regard to old liquors, it is known that ammonia is a powerful aid to the unhairing process, and it is not certain to what extent the liquors he used were charged with it. It is also certain that old limes containing much organic matter, support bacterial life freely, while 25 per cent. of a possibly not very old liquor would probably be sterilised by the addition of lime and 75 per cent. water. In order to test the matter fairly under exact tannery conditions, the lime should have been made up entirely with old lime-liquor well charged with ammonia and organic matters, instead of with water. It is also probable that the hides had undergone a sufficient amount of bacterial change in the tannery before they came into Von Schroeder’s salt solutions, and it is not at all unlikely that the salt solution itself exercised some specific effect on the unhairing. It is also possible that his bacterial cultures were made on gelatine media unsuitable for the growth of alkaline bacteria, and therefore gave blank results. Under these circumstances it is scarcely possible to arrive at any very definite conclusions, and it is obvious that further experiments on these points are extremely desirable.