The leech is a fresh-water parasitic invertebrate belonging to the Phylum Annelida. On one end of its worm-like body is a large sucker by which the animal fastens itself to the ground, and at the other end is a smaller sucker, in the middle of which is a chitinous mouth that makes a triangular puncture. As items of _materia medica_, leeches were described in dispensatories, or compilations of medicaments, and sold by apothecaries, both to physicians and directly to patients. The species most commonly used for bleeding was _Hirudo medicinalis_, indigenous to the streams and swamps of Central and Northern Europe, and known in commerce as the Swedish or German leech. It was 50-75 mm long, with a dull olive green back and four yellow longitudinal lines, the central two broken with black. Somewhat less popular was the Hungarian leech, indigenous to Southern Europe. In addition, there was an American species of leech, _Hirudo decora_, which was gathered principally from the lower Delaware River, but, since it drew much less blood than the Swedish leech, it was regarded as greatly inferior.[173] Most American physicians imported their leeches. In the late nineteenth century, one could buy Swedish leeches for $5.00 per hundred.[174] Leeches were gathered in the spring of the year either by means of a pole net, or, more primitively, by wading into the water and allowing the leeches to fasten themselves onto the legs. Sometimes horses and cattle were driven into the water to serve as bait for the leeches.[175] (Figure 19.) [Illustration: FIGURE 19.--Lithograph published in London in 1814 showing three women gathering leeches by a stream. (NMHT 320033.08; SI photo 76-7741.)] Leeching, like other forms of bloodletting, enjoyed a revival in the early nineteenth century, particularly in France, where the doctrines of heroic medicine preached by Broussais[176] led to an increase of leech usage from about 3 million in 1824 to 41.5 million in 1833.[177] Leechers, although not as high in status as professional cuppers, practiced in many large cities, and numerous tracts were written on the care and breeding of leeches. "Leech farms" were unable to increase the leech supply to meet the rising demand, and most leechers complained of the scarcity and great expense of the little animals.[178]