Poison pen
I鈥檝e been reading a book called Deadly Doses: A writer鈥檚 guide to poisons and it has raised two questions. When I was at school, my biology teacher told the class it was possible to drink snake venom and survive, because the venom is a protein and would be broken down by the digestive process. Yet the book says snake venom is deadly if taken orally. Who is right? And is it possible to build up a tolerance to arsenic, as in Dorothy L. Sayers鈥檚 book Strong Poison, and so survive a lethal dose?
鈥� Readers should be aware that there seems to be no consensus on what is safe. One thing is certain: these substances are dangerous and should be treated with extreme caution and not ingested in any form 鈥� Ed
鈥� I have watched a Zambian snake expert, Major Alick Chanda, milk the venom from a live puff adder (Bitis arietans) into a wine glass and drink it, with no ill effects.
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Snake venom is a complex mixture of proteins, the composition varying from species to species. It can be classified into three major groups: cytotoxic, which attacks cells and tissues and is produced by vipers and adders; neurotoxic, which affects the nerves and is produced by cobras and mambas; and haemotoxic, which affects the blood-clotting process and is produced by back-fanged species such as the boomslang and bird snake. Whatever the type, the venom has to enter the bloodstream to have an effect. That is why snakes bite with hypodermic-like fangs. If you swallow venom, provided you have no lesions in your gastrointestinal tract, the proteins will be broken down into harmless amino acids and absorbed, like the products of all protein digestion.
Arsenic is an entirely different matter. Being an element it is not affected by the digestive process. It is poisonous in doses of as little as 65 milligrams, and the poisoning can arise from a single large dose or from repeated small doses as, for example, by inhaling arsenical gases or dust, or drinking contaminated water.
There have been various accounts of people acquiring tolerance to poison by repeated small doses. In the 2nd century BC, King Mithridates IV was reputed to have used this method so successfully that, when he tried to commit suicide by swallowing poison after defeat in the Battle of Pompey he failed 鈥� and had to be stabbed to death. And Rasputin reportedly swallowed the stuff regularly to protect himself from being bumped off.
However, the physiological basis for such a tolerance has never been ascertained, and arsenic is known to be carcinogenic in small quantities. One has only to look at the effect of small repeated doses on the unfortunate inhabitants of Bangladesh, whose wells are contaminated with it, to see this is harmful and ultimately fatal.
Alistair Scott
Gland, Switzerland
鈥� Here in the US, roadside and entertainment park exhibitions where snake handlers would handle venomous reptiles were once commonplace. In one of the most notorious, Ross Allen of Florida milked rattlesnakes into a glass and afterwards drank it. He never exhibited any obvious ill effects, although he did say the venom made it 鈥渉ard to whistle鈥� for sometime afterward.
Very high concentrations of venom given to animals orally, however, can have lethal consequences. The amount of venom administered for this experimental purpose is almost as much as the stomach can hold. If administered intravenously, these doses would be tens of thousands of times the LD50 鈥� that is, the amount of venom that kills 50 per cent of a group of lab animals. When given orally, death is the result of the venom itself and not a by-product of its digestion 鈥� administering antiserum saves the animal.
Professor Joseph F. Gennaro, Jr (retired)
University of Florida College of Medicine Gainesville, US
鈥� It is possible to build up a tolerance to arsenic and survive a dose that would normally be lethal.
Arsenic is toxic because it binds to, and thus inactivates, proteins that are essential to metabolism. However, it can be inactivated in the body by enzymes called metallothionines, and the presence of arsenic can induce liver cells to produce more of these. If small quantities of arsenic are consumed over a period of time, then enzyme production will be induced more often and background levels will increase.
This is the same sort of mechanism that allows alcoholics to consume quantities that would kill a teetotaller.
Craig Fitzpatrick
Estcourt, Western Australia
鈥淩asputin reportedly swallowed arsenic regularly to protect himself from being bumped off鈥�
鈥� Only a fool would drink venom, because dangerous doses can get into the circulation through minor injuries to the mucous membrane of the digestive tract.
Many venoms contain enzymes that damage tissues and let poison in, and though toxic proteins certainly are deadlier when injected, some do pass through the gut wall. This factor is more important in infants, but even adults can die of swallowing small doses of very poisonous proteins, such as ricin. Gut enzymes break down some of the most dangerous venoms too slowly to give much protection, and many venoms resist or inhibit some of our digestive proteases.
As for inorganic arsenic, claims of tolerance are confused by travellers鈥� tales, quackery, ill-defined preparations and personal variation. Chemistry affects toxicity (arsenites are more poisonous than, say, arsenates or sulphur compounds) and the gut absorbs coarse-textured, poorly soluble material less easily. Soluble arsenic, far from inducing tolerance in small doses, is dangerously cumulative.
Dorothy L. Sayers鈥檚 jam omelette story was cute, but before a would-be murderer had managed to kill anyone by this method, he would probably have expired.
Jon Richfield
Somerset West, South Africa
This week鈥檚 questions
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In the movie X-Men, part of the human race spontaneously turns into mutants with incredible powers. Is it at least theoretically possible for this to happen, perhaps via a virus that could inject its DNA into the human genome?
Samuel Hopkins
By email, no address supplied
Finding Nemo鈥檚 flies
I was walking outside during a recent heatwave in Sydney, swatting all the newly hatched flies and contemplating how much of the Earth鈥檚 biomass is accounted for by insects, when it occurred to me that I have never heard of any insects that live in or on the sea. Are there any?
Rob Moore
Sydney, Australia