Sponges, of which there are very many varieties, inhabit the bottom of the sea, where they are fixed to rocks. The best are obtained from the Mediterranean and Red Seas, inferior qualities from the West Indies.

Description. Sponge is prepared for use by steeping it for some days in cold water, the concretions which it contains being separated by occasional beatings. It is afterwards washed in water acidulated with hydrochloric acid, by which the remainder of the earthy particles are removed: in addition, it is often bleached with sulphurous acid. The general appearance of the sponge is too well known to need description. When burnt, sponge yields the article, formerly officinal, termed spongia usta, which occurs as a blackish-brown powder.

Prop. & Comp. Sponge consists of gelatinous matter, and various salts of lime, potash, magnesia, etc. Burnt sponge contains a large amount of carbon, mixed with carbonate and sulphate of lime, chloride of sodium and iron; also from 1 to 2 per cent. of iodide of potassium, with some bromide. It is upon the presence of these latter constituents that its medicinal properties depend.

Therapeutics. Spongia usta, or burnt sponge, has been much recommended in goitre and strumous glandular swellings, in which cases it is still sometimes given. In addition to its use for domestic purposes, sponge is sometimes used in the form of a tent.

Dose. Of burnt sponge, 30 gr. to 100 gr. or more, made into an electuary, sometimes given in lozenges.