venom or zootoxin, any of a variety of poisonous substances produced by animals. In poisonous snakes, venom is secreted in two poison glands, one on each side of the upper jaw, and enters the fang by a duct. Snake venom is a complex substance, containing various enzymes and toxins. Venoms differ in their effect according to the preponderance in them of hemotoxic, hemolytic, or neurotoxic agents. Hemotoxins perforate the blood vessels, causing hemorrhage, and hemolysins dissolve the red blood cells. The venom of the fer-de-lance is chiefly hemotoxic; that of the rattlesnake, the copperhead, and the moccasin is both hemotoxic and hemolytic. Neurotoxins produce paralysis, often of the nerve centers that control breathing, thus causing a quicker death from suffocation. Cobras, coral snakes, scorpions, and spiders produce neurotoxic venoms. The venom of the gaboon viper is both hemotoxic and neurotoxic. Venoms may also contain agglutinins, which promote coagulation of blood, or anticoagulants, which have the opposite effect. The venoms of various snakes have been used medicinally, according to their specific properties, as painkillers (in arthritis, cancer, and leprosy), antispasmodics (in epilepsy and asthma), and blood coagulants (in hemophilia). The venom of the Russell's viper has been used as a coagulant in tonsillectomies and for bleeding gums. The effect of any snakebite necessarily depends on the quantity and kind of toxin it contains, as well as on the resistance of the victim. Immune serum against snake venom, or antivenin, can be prepared by repeatedly injecting sublethal doses of venom into an animal such as the horse. The immune serum thereby produced in the animal can be extracted and used to treat snakebite victims. Poisons are produced by animal species of every phylum; examples include the poison in the rounded warts of the skin of toads, the venoms of spiders, scorpions, bees, and other arthropods, and the poison of jellyfish and other coelenterates. See also toxin.