Page:An introduction to pharmacognosy (1905).djvu/16

 ANIMAL DRUGS.

As the science of medicine has progressed step by step, the great number of drugs derived from the members of the animal kingdom has been reduced. This large number of drugs was gradually introduced during the middle ages, so that in the middle of the sixteenth century at least 150 drugs derived from some portion of an animal were in constant use.

In the days of Hippocrates II, 400 B. C., and Dioscorides, 50 A. D., very few such drugs were employed, and at the present time the number is very small, except in the homeopathic Pharmacopœia, where many of the materials in use during the middle ages have been retained.

Certain animal drugs have maintained their reputation for efficiency, and only a few of these will be considered. HIRUDO. THE LEECH. This is a worm of the Annelid or Ringed-worm class. The most familiar one of the class is the Hirudo medicinalis, and this is the variety most commonly used. It lives in ponds and slow-flowing streams, where it feeds upon the blood of fishes, frogs, snails and other available food materials. It is its habit to take as much at one time as possible, gorging itself upon what supply of food is obtainable. It can thus often live a whole year without feeding twice. Its mode of locomotion is by means of the alternate use of the front and rear suckers, and when disturbed it swims by a rapid wave-like motion of the entire body.

Description.— The leech usually measures from 5 to 15 centimeters (2 to 6 inches) in length and is either 20