COMMENTARY. What this substance was is well stated by a comparatively recent writer on the Materia Medica. Dr. Lewis, treating of zinc, says, “Moderately pure white flowers sublimed from it in the brass or other furnaces, wherein zinc, or its ores are melted with other metals, were formerly kept in the shops and distinguished by the names of pompholix and nihil album.” (Mat. Med. ii, 485.) A still later authority on the Pharmacopœia describes it thus: “_Pompholix Nihil album._ Collected in the smelting furnaces wherein zinc ores or brass are melted; used in ointments for tutty.” Gray (Suppl. &c. 234.) It is also distinctly described by Geoffroy (Treatise on Fossil, &c. Subst. 185), and by Quincy (201.) The latter writes as if he had been familiar with this article; but it appears singular that the former says that in his time (that is to say, about 150 years ago) it was unknown in the shops. For the ancient authorities on it, see in particular Pliny (H. N. xxiv, 33), and Dioscorides (v, 85.) The latter calls it styptic, cooling, and to a certain extent escharotic. Galen recommends it in carcinomatous and all ill-conditioned ulcers, for those about the parts of generation and anus, and for ocular collyria. (De Simpl. ix.) The Arabians treat of it under the head of Tutia. See in particular Serapion (c. 422); Avicenna (ii, 2, 695); Averrhoes (Collig. v, 43); Ebn Baithar (i, 217.) Hardly one of them does anything more than copy the description of it given by Dioscorides and Galen, only comprehending under one name what the Greeks had delivered regarding pompholyx and spodium separately. Πορφύραι, Purpuræ, when burnt are possessed of the same powers as shells. The part which serves as a cover to them when boiled in oil, strengthens hairs that are falling out. When drunk with vinegar, they cure swelling of the spleen. As a fumigation, they rouse in cases of uterine suffocation, and expel the secundines. * * * * * COMMENTARY. The shell-fishes which supply the purple dye. It is got from various fishes, but more especially the _Helix ianthina_, _Murex brandaris_ and _trunculus_. For an account of them, see particularly Aristot. (Hist. Animal. v, 14), and Pliny (H. N. ix, 60.) Our author borrows from Dioscorides (iii, 4), and Galen (De Simpl. xi.) We have not been able to detect this article in the works of the Arabian authorities. Ποταμογείτων, Potamogiton, _Pondweed_, is cooling and astringent, like Polygonum, being possessed of similar powers to it. * * * * *