Free Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance by Kenneth Kamler

risk in order to decide whether using up venom is necessary. When humans are envenomated, it is almost always because the snake felt mortally threatened, from being stepped on or poked at. Snakes do not want to waste their venom on humans, which are not prey. Because a snake’s teeth point backward, they are good only for gripping; snakes can’t tear apart or chew their prey, and humans are too big to swallow whole.
    Venom is a mixture of poisons and of enzymes, substances thatdissolve body tissues. Each kind of snake makes its own variety; the effect of venom inside the body therefore depends on its individual recipe. The coral snake I met near the latrine uses mostly nerve poison, while the snake that slept with Antonio prefers to poison the blood. Both types are quick and deadly because they attack the body at its weakest points—the fragile chemical reactions critical to the dynamics of breathing, heartbeat, and blood clotting.
    Muscle contractions make hearts beat and lungs breathe. Muscles are powerful machines that can sustain a lot of damage and keep on going. But like a lot of machines, they will stop cold when unplugged. They depend on the constant supply of electricity that reaches them through the wiring system of the nerves. Small spaces exist between each consecutive nerve and between the nerve and the muscle. When the current comes to the end of a nerve, it faces a gap it has to jump if it is to continue. The nerve end releases a chemical called a neurotransmitter that floats across the gap and sparks the next nerve. The last nerve before the muscle ends in a group of tendrils, like a multipronged plug, that align with but don’t quite connect to a corresponding socket in the muscle. Another neurotransmitter has to float a connection between the two. It is precisely this last delicate step that the coral snake’s venom blocks. The venom mimics the neurotransmitter and fills the gap, but it does not conduct the signal. The transmission of electrical impulses is interrupted; muscles fire irregularly, then weaken, and finally become paralyzed. The victim twitches, collapses, and loses the ability to speak. Within a few hours the paralysis overtakes the pulmonary and cardiac muscles. The lungs stop breathing and the heart stops beating.
    The pit viper uses a different but equally lethal technique. Its poison weakens the walls of blood vessels, allowing blood cells and fluid to leak into the surrounding tissues. Whenever a blood vessel is breached, the body’s natural defense is to set off a cascade of reactions that convert free-floating raw materials into a sticky mesh that forms a clot to seal the hole. That process, known as coagulation, is why a cut stops bleeding. Pit viper venom sabotages the intricate sealing process with an ingredient that mimics one of the crucial raw materials and gets itself incorporated at an early step. It is much weaker thanthe real thing, so the final clot ultimately gives way. The mesh cannot form a seal strong enough to stop the bleeding. It is a fatal weakness: the blood goes everywhere but where it belongs, filling the lungs and emptying the heart.
    Because venoms are thick, they contain an additive, hyaluronidase, that helps diffuse their poisons. Doctors routinely add this dissolving enzyme to injected medicines to increase the rate of absorption. Snakes use it to speed up the spread of their venom. Snakes also inject another enzyme that digests muscle. It causes the severe tissue destruction often seen at the site of a bite, but its real purpose is to give the snake, which cannot chew, a head start on its anticipated meal.
    Treating someone who has been on a snake’s menu is not easy. If he has been envenomated, he will probably die. Venom is not a single poison; one injection is similar to a multidrug overdose. The catastrophic breakdown of many organ systems that rapidly follows the poisoning is hard to reverse, even in the most sophisticated hospital. In the jungle it