Harvey的阅读回忆：眼镜蛇毒

　　The king cobras deadly fangs are almost half an inch long. Because they are fixed to the upper jaw, they have to be short. If they were longer, the king might bite the floor of its mouth and commit royal suicide. Angled back into the snakes mouth, the fangs help push the prey on its path to the stomach. A regal bite delivers venom from glands attached to the fangs. The flexing of a small muscle forces the venom through the hollow fangs into the victim.

　　Within minutes, neurotoxins stun the preys nervous system, especially the impulses for breathing. Other toxins start digesting the paralyzed victim. Drop for drop, a king cobras venom is actually less lethal than a common cobras. The king more than makes up for it by delivering more venom per biteas much as .2 fluid ounces of liquid. Thats enough to kill an elephant, or 20 people.

　　About Venom

　　Snake venom is produced by special cells in two large venom glands on each side of the head. Out of 3,000 known species of snakes, more than 500 are venomous. The 10 most lethal snakes in the world belong to the elapids--often called the cobra family. Cobra venom kills via neurotoxins, proteins that paralyze an animals nervous system and diaphragm, abdominal muscles used to breathe. The snake metes out the exact amount of venom needed to suffocate the prey, then swallows its catch. Headfirst. The proteinaceous nature of snake venom was established by Napoleon Bonapartes brother, Lucien in 1843. Proteins constitute the major portion of venoms dry weight90% or more. Snake venom is a cocktail of hundreds, sometimes thousands, of different proteins and enzymes. Many of these proteins are harmless but a percentage of them are toxins. The makeup of these toxins varies widely from species to species. This complexity accounts for the widely differing effects of snakebite.

　　Venoms are rich in hydrolithic enzymes, a complex mix of polypeptides, nucleases, peptidases, etc., which help digest the snakes prey. Some of them also enhance or contribute to the toxic effect of the venom. As early as 1949 it was shown that an enzyme from the Bothrops species produces a vasodilation resulting from the production of a hypotensor neuropeptide, bradykinin. This had important consequences for man leading to drugs for the control of blood pressure.