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There are about 2,700 species of
snake living on the earth today, of which about 400 posses fangs and other
venom apparatus. Even the harmless snakes, however, often have
digestive enzymes and mild toxins in their saliva. These have a
numbing effect on the preferred prey of the snake, and help the snake
obtain food. In rare cases, these mild toxins can produce symptoms
in humans. |
| Only about 200 species of snake are
potentially dangerous to humans. Drop for drop, the most powerful
venom among terrestrial snakes belong to the Inland Tiapan and the Tiger
snake, both Australian elapids. Among the vipers, the most powerful
venom is that of the Saw-Scaled Viper. The sea snakes, members of
the elapid family, have even more powerful venom than their terrestrial
cousins( they need it as their prey must be killed quickly before it can
swim away ), but they are only rarely encountered by humans. |
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Snake venom consists of a large number
of components, nearly all of which are proteins manufactured in the snake's
venom glands. Among the various types of proteins found in snake
venom are proteolysins, which break down cell walls and destroy body
tissues and blood vessels; hemorrhagins, which break open blood vessels
and cause internal bleeding; cardiotoxins, which attack the muscles and
nerve centers of the heart; and cytolysins, which attack and break down
white blood cells. |
| There are two basic types
of snake venom. Hemotoxic venoms contain a high proportion of
proteolysins and hemorrhagins, and work by breaking down the capillary
walls and destroying body tissues, leading to massive internal bleeding
and organ damage. Bites from a hemotoxic snake are extremely
painful, and often lead to such tissue damage that amputation of toes or
fingers is sometimes necessary in survivors. Neurotoxic venoms, in
contrast, attack the central nervous system by interfering with the
transmission of nerve impulses. Because there is little tissue
damage, bites from a neurotoxic snake are relatively painless, but produce
a deadening effect somewhat similar to alcohol. The victim feels as
if he is falling asleep. Death comes when the muscles that power the
lungs and heart are paralyzed, asphyxiating the victim. Both types
of toxin are found in most snake
venoms. The neurotoxic elements paralyze the prey animal and disable
it, while the hemotoxic components serve as "meat tenderizers"
that break down the body tissues so that they can be more easily
digested. In general, the vipers and pit vipers are predominantly hemotoxic in action, while the elapids are largely neurotoxic. There
are exceptions, however, the Mojave Rattlesnake, a pit viper, has venom
that is largely neurotoxic, while the Australian Death Adder, and elapid,
has hemotoxic venom. Although some species of snake are indeed
capable of killing an adult human, for most part the dangers of snake
bites are greatly exaggerated. Almost four times as many people are
killed worldwide by bee stings than by venomous snakes. More people
are struck by lightning each year than are killed by snakes. Many
snakes will defend themselves with a "dry bite", in which no
venom is injected. On average, about one in three bits is dry.
In about one-third of the cases where venom is actually injected, it is such a small amount that no clinical symptoms occur and no damage is
done. Even in cases where full envenomation takes place and the bite
is untreated, death only occurs on average on our of eight
times.
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