Lead frit is a constituent of low-solubility glaze--that is to say, a glaze which has not more than 5 per cent. soluble lead when subjected to the standard test of exposing 1 gramme of the glaze to a litre of 0·04 per cent. hydrochloric acid for an hour at room temperature. The frit which was the constituent of this glaze is produced by heating together litharge or lead and silica, the production being a yellow, hard, glaze-like material looking very much like sugar-candy. It is not by any means a compound of lead and silica of simple composition, as different samples show a wide variation in their lead content; whilst, in addition, the mode of its formation closely resembles that of an alloy or amalgam, and allows of the formation of a eutectic entangling in its meshes both of the constituents of which it is formed, so that a certain amount of free lead, in addition to the silicates of various descriptions, are present. At the same time the compound is highly resistant to the action of mineral acids, and, of course, much more insoluble and refractory than white lead, litharge, or other lead oxides. The body fluids, however, particularly the fluids in the subcutaneous and muscular tissue, definitely exert some action upon this fritted lead, and it was found experimentally that symptoms of poisoning could be produced in the experimental animals when even small doses were administered. A gramme of frit was inoculated, and in all but one case the animals showed definite signs of lead poisoning, and in two instances actually died with symptoms of encephalitis. By washing the frit with distilled water, a slight diminution in the poisonousness was found, but by washing the frit with two or three changes of dilute acetic acid (3 per cent.), and then with distilled water, no pathological results followed inoculation. Water-washing frit alone definitely reduces the poisonous effect, but not to the same extent as the preliminary washing with acetic acid. On the other hand, washing with hot water had a much greater effect than cold-water washing. Further evidence given by the inoculation experiments shows the relationship between the more soluble and the insoluble lead salts. The dose of acetate required to kill an animal was about 0·1 gramme of acetate per kilogramme body weight. On the other hand, 0·1 gramme of white lead produced no ill-effects, 0·5 gramme per kilogramme body weight produced death in about two months. In addition, those animals suffering from the more acute forms of poisoning developed definite eye changes and retinal hæmorrhages. Tortuosity and increased size of the retinal vessels were observed in several instances.