In making comparative tests of my artificial bates and dog dung, I usually took the latter from the paddles in which it was diluted ready for use, and maintained both solutions at exactly the same temperature. Parts of the _same_ skin were then digested in each solution, and the results noted after 1-1/2 hours. In order to make them more strictly comparable I filtered the dung bate, so as to employ the matter actually in solution when the bate was made up. It was found that the filtered bate had far less action than when it was used in an unfiltered condition. That this is not wholly due to the passing into solution of some of the solid matter during the bating was shown by adding an inert solid, viz., kaolin, to the filtered bate, when the action was greatly hastened. On adding kaolin to the artificial bate and keeping the liquid agitated, the same result was obtained. It seems that the finely-divided solid matter acts as a carrier for the enzymes, perhaps by a kind of mass action, each particle offering a surface vastly greater than the molecules of dissolved solids. In the case of “puer,” the organic insoluble matter is gradually brought into solution by bacterial action as the bating proceeds, though I do not believe this occurs to any great extent. The following quantities of soluble and insoluble matter were found in puer wheels in actual practice per 100 c.c.:-- -------------+-------+------+------+------ ---- | 1 | 2 | 3 | 4 -------------+-------+------+------+------ Total solids | 10·20 | 8·63 | 8·64 | 3·26 Soluble | 6·00 | 4·57 | 6·19 | 2·14 Insoluble | 4·20 | 4·06 | 2·45 | 1·12 -------------+-------+------+------+------ 1. Wheel in constant use for a week. 2. Wheel freshly made up. 3. The same wheel after one lot of skins. 4. From pigeon dung bate pit. On comparing 2 and 3 it will be seen that apparently 1·61 grm. of the insoluble matter has passed into solution. This is not entirely the case, for part of the additional soluble matter is lime and hide substance from the skins, while part of the insoluble at the same time adheres to the skins and is not estimated.