Attention has been given to the solubility of lead salts in gastric juices, the majority of such experiments having been performed with artificial gastric juice. The method at present in use, prescribed by the amended rules of August, 1900, for earthenware and china factories, is based on some, if slight, consideration of the physiology of digestion. The method described by Rule II. states that the estimation of the quantity of lead present in the lead fritt shall be performed as follows: A weighed quantity of dry material is to be continuously shaken for one hour at room temperature with one thousand times its weight of an aqueous solution of hydrochloric acid, containing 0·25 per cent. of HCl. This solution is thereafter to be allowed to stand for one hour, and to be passed through a filter. The lead salt contained in a portion of the clear filter is then to be precipitated as lead sulphide, and weighed as lead sulphate. This method has been adopted on the supposition that the solubility of a lead salt in the gastric juices is the chief source of the lead poisoning in the Potteries, and that the hydrochloric acid content of the solution determines, for practical purposes, the quantity of lead dissolved out of a given sample. The temperature, however, at which this estimation is made--namely, room temperature--is one considerably lower than that of the body, and the quantity of lead taken up into solution at this temperature is less than that which occurs at the ordinary temperature of the body--37° C. Practically twice as much lead is dissolved out of fritt at 37° C. for an hour as is rendered soluble at the ordinary temperature of the room--about 15° C. Thomason[11], who made some experiments in this direction, gives a figure of 2·35 lead oxide dissolved at 15° C. and 4·54 at 37° C. In another estimation--a matter, too, of some considerable importance--it was found that acetic acid dissolved 1·97 per cent, at 15° C., and 3·27 at 37° C. In lactic acid the figure was 2·28 at 15° C., and 3·53 at 37° C. It is therefore a low estimation of the solubility of any substance by the gastric juices if the substance is operated on at a temperature below that of the body. The question of the solubility of a lead salt in the gastric contents is important in view of the small quantities of dust swallowed; and in addition to hydrochloric acid, other substances are also present in the gastric juice, which is by no means a simple aqueous solution of the mineral acid. Further, the gastric juice, except in cases of pathological type, is not acid in periods of gastric rest, unless such acidity may be represented by the presence of fermentative acids--acetic, lactic, and butyric.