608. HIRUDO.—LEECH. Sanguisu'ga medicina'lis Savigny. Class, Vermes; order, Annelida; family, Hirudinea.
HABITAT.—Northern and Central Europe chiefly, but found more or less in all parts of Europe, in ponds of fresh water.
DESCRIPTION.—The body, which varies in length from 75 to 150 mm. (3 to 6 in.), is smooth and round, tapering toward both ends, and made up of about 100 soft rings or folds. Both ends are provided with a flattened disk, the posterior being the larger, each of which is adapted to fix upon objects by suction. The mouth has three jaws, with a double row of fine sharp teeth in each; the small anal opening is found on the under side of the last posterior wrinkle. Color of black greenish and striped longitudinally with numerous black spots; belly somewhat lighter green.
OTHER SPECIES.—Besides S. officinalis, which is next to S. medicinalis in importance and is similar in appearance (only there are no spots, and a black line extends along each side), may be mentioned Hirudo provincialis, H. obscura, and H. interrupta, the species common in this country being known as H. decora. Leeches are said to be found in great abundance throughout India.
PRESERVATION.—The usual way of keeping leeches is to place them in clear water, in a shaded spot if possible, where the temperature will range from 10° to 20°C. (50° to 68°F.), care being taken to have a considerable quantity of charcoal, moss, and pebbles in the containing vessel.
USE.—For local blood-letting, a single leech being able to extract from 1 to 2 drachms of blood.