in fabulous history, a serpent in the marsh of Lerna, in Peloponnesus, represented by the poets with many heads, one of which being cut off, another immediately succeeded in its place, unless the wound was instantly cauterized. Hercules attacked this monster; and having caused Iolaus to hew down wood for flaming brands, as he cut off the heads he applied the brands to the wounds, by which means he destroyed the hydra. This hydra with many heads is said to have been only a multitude of serpents, which infested the marshes of Lerna near Mycene, and which seemed to multiply as fast as they were destroyed. Hercules, with the assistance of his companions, cleared the country of these reptiles, by burning the reeds in which they lodged.
in Astronomy, a southern constellation, consisting of a number of stars, imagined to represent a water serpent.
HYDRAGOGUES, amongst physicians, remedies which evacuate a large quantity of water in dropsies. The word is formed from ὕδωρ, water, and ἄγειν, to draw or lead; but the application of the term proceeds upon a mistaken supposition that every purgative had some particular humour which it would evacuate, and which could not be evacuated by any other. It is now, however, discovered that all strong purgatives will themselves prove hydragogues, if administered in large quantity, or to persons of weak constitutions. The principal medicines recommended as hydragogues are, the juice of elder, the root of the iris, soldanella, mechoacan, jalap, &c.
HYDRARGYRUM, a name given to mercury or quicksilver. The word is formed from ὕδωρ, aqua, water, and ἀργυρος, argentum, silver, water of silver, on account of its resembling liquid or melted silver.
HYDRAULICS, the science of the motion of fluids, and the construction of all kinds of machines relating thereto. See HYDRODYNAMICS.
HYDRENTEROCELE, in Surgery, a species of hernia, in which the intestines descend into the scrotum, together with a quantity of water.
HYDROCEPHALUS, a preternatural distension of the head by a stagnation and extravasation of the lymph, which, when collected in the inside of the cranium, is termed internal, as that collected on the outside is termed external. See MEDICINE, Index.
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1 See Visit to the Court of Sinde, by J. Burnes, p. 92.
a large sea-fish, which is said to have been destroyed by Moses in the Red Sea. It is supposed to be the same as the sea-serpent mentioned in Exodus 7:12.
a genus of plants, some of which produce a large quantity of water-drops. They are found in the sea, and are known as sea-drops or sea-eyes. The application of the term proceeds from a natural affinity that every purgative had some virtue by which it would eradicate, and which could not be cured by any other. It is now, however, discovered that purgatives will themselves prove productive of constipation. The principal medicines recommended for this purpose are the juice of cider, the root of the mallow, or chamomile, juniper, &c.