It might seem odd to bundle a discussion of poison in with our exploration of medicine, but as the sixteenth-century Swiss physician known as Paracelsus said, “All things are poison, and nothing is without poison; the dosage alone makes it so a thing is not a poison.”
Paracelsus was a pioneer in the use of chemistry in medicine, and the idea that physicians ought to understand the basics of that field. His ideas weren’t completely modern — he leaned heavily on the principles of hermeticism, too, developing them into his own equivalent three-humor framework — but he believed in the importance of antisepsis (rather than assuming that infection was a natural and even desirable part of the healing process), and he understood that not only could poisonous substances sometimes have benefits, but beneficial substances could also be dangerous.
Think of foxgloves. This genus of flowers contains a chemical that’s useful in treating cardiac problems — but if you want to give your patient a heart attack instead, all you have to do is feed them more than the useful dosage. Heck, even drinking too much water can kill you, by disrupting the balance of your electrolytes until your brain shuts down. On the flip side, I mentioned mercury treatments for syphilis before; they weren’t a great treatment, not least because their side effects were so terrible . . . but then again, having syphilis wasn’t great, either. The modern comparison might be chemotherapy, which amounts to attempting to poison a cancerous tumor without killing the patient around it.
But determining the proper dosage can be a tricky challenge, because a host of factors can affect how someone metabolizes a given medication, and what side effects they show. And I mentioned the placebo effect before, but we’re also starting to pay attention to its counterpart, the nocebo effect: just as someone is more likely to get better if they think they’re taking medicine, knowing about a possible side effect makes it more likely that you’ll experience it.
As you might imagine, this makes things complicated for physicians. This is probably why the laws of Tang Dynasty China made it a crime for a physician to diverge from the instructions given in medical texts when treating the emperor. Hewing to the advice therein might still fail to work, cause unpleasant side effects, or even result in the emperor’s death . . . but being able to say “I followed the instructions to the letter” is a form of protection. A doctor who experiments with something new might be acclaimed if it works, but if it doesn’t, he’s at high risk of being accused of having killed his patient.
Of course, sometimes that was the goal. I’m not going to attempt to give a comprehensive overview of the types of poison (here taken in the sense of “things normally used to kill someone,” not medicines you can overdose on); if you want details on that, Writer’s Digest published a book years ago called Deadly Doses: A Writer’s Guide to Poison. Mithridates VI, King of Pontus, famously consumed sub-lethal doses of various toxins to build up an immunity after his father was poisoned at a banquet in 120 B.C., as immortalized in a poem from A.E. Housman’s collection A Shropshire Lad.
Poison often had a reputation of being “a woman’s weapon” — by implication, the weapon of weaklings and cowards. It’s admittedly an underhanded maneuver, but as Book View Cafe’s own Nancy Jane Moore has pointed out, the people in power (e.g. strong, armed men) also tend to set the rules in a fashion that favors their advantages. Consequently, anything which circumvents those advantages gets characterized as contemptible or outright evil. Poison doesn’t require muscles or facing your opponent directly, and therefore is useful to people that deck has been stacked against.
Once poison has gotten into your system, there may or may not be much you can do about it. Sometimes inducing vomiting can help, by expelling the poison before it fully takes effect. In other cases a physician might be able to alleviate the symptoms well enough to keep the patient alive until the poison runs its course. But prior to modern medicine’s antitoxins, and even sometimes with those, many poisons leave you in a state where your only real recourse is to pray.
(By the way — because I screwed this up at one point while writing the Memoirs of Lady Trent, which was embarrassing when my narrator was a natural historian — “poison” and “venom” aren’t synonyms. Poisons are ingested; venom is injected by a bite, sting, or other attack. It’s still risky to consume, because you may have open cuts or ulcers in your mouth or throat or stomach, but not in the same way as if it gets directly into your blood.)
Since treating poison after it had been ingested was so difficult, a lot of effort went into prevention instead. Kings and other important people might employ “tasters,” people whose job was to sample their food and drink ahead of time. Some poisons carry a distinct enough taste, or cause sensations like numbness in the mouth, that a trained person with a good palate can notice them before a lethal dose is consumed. Failing that, waiting a few minutes to see if the taster shows any adverse effects could warn the king in time for him not to dig in.
People weren’t the only means of detection, though. Silver tarnishes in the presence of some poisons, so it wasn’t just the ostentation of using precious metal that encouraged the wealthy to use silver spoons. The horn of a unicorn — generally a narwhal tusk — could be touched to food or drink, and according to tradition the latter would begin to smoke if it was tainted. Toadstones, which are actually ancient fish fossils, were worn against the skin and likewise supposedly heated up or changed color in the presence of poison. Alternatively, you could focus on neutralizing the threat before you consumed it, for example with emeralds or (much less attractively) with bezoars, masses sometimes found in the intestinal tract.
Narratively — and to some extent in history — the use of poison is characteristic of aristocratic societies with a lot of backstabbing intrigue. The Borgias in Renaissance Italy in particular had a reputation for using it to eliminate their enemies. But in some ways its real heyday was the late nineteenth and early twentieth centuries, when the sudden boom in industry made a huge variety of toxic chemicals widely available to the common citizen, and there wasn’t yet much capacity for detecting when a death was caused by poison. (For more information on that, check out The Poisoner’s Handbook: Murder and the Birth of Forensic Medicine in Jazz Age New York, by Deborah Blum.) Which is why, both in the past and in fiction, poison is often the ideal method for surreptitious murder.