Agatha Christie and Her Poisons

Chemist-turned-writer Kathryn Harkup talks to Science Friday

ON DISCOVERING AGATHA CHRISTIE:

I loved Christie when I was a teenager. I was reading her brilliant stories, very engaging, easy-to-read stories that have fantastic puzzles, as your introduction shows. You always have this cast of characters, fantastic clues, and you always think to yourself, I should be able to work this out, this is not beyond the wit of man, but of course I always get to the end of the novel and I was never correct in guessing. I am absolutely flawed in my ability to get whodunit in an Agatha Christie. But I loved her stories, so my Agatha Christie fandom stretches way back and chemistry came in much later.


“Agatha Christie” by Agatha Christie plaque — Torre Abbey

THE DEATH TOLL OF A WRITER:

Christie killed over 300 people, fictionally obviously, and at least 100 of those were killed by poisons but not just your imaginary, made-up, untraceable poisons. I think her toxic tally is over 30 different compounds, which is incredible and they are all brilliantly integrated into the plot so there’s lots of chemistry and biological clues in there, if you’re looking for them.


CHRISTIE’S POISONOUS EXPERTISE:

During World War I, she volunteered as a nurse in her local hospital, but it was suggested that she might want to work in the hospital dispensary. And this was a time, 1914–1918, when all drugs, pills, tonics, creams, etc. — they were made up by hand — so she had to do a lot of studying in chemistry, both theoretical and practical, to make sure that she got the right dose and she didn’t mix the wrong drugs to hand out to people. It was also a time when lots of compounds that you just cannot get ahold of today, were still being prescribed as medicines. It was a good time to be a poisoner, it was not such a good time to be on the receiving end of some of these drugs.

Drawings of “Atropa belladonna” and “Digitalis purpurea.” From Köhler’s Medicinal Plants, via Wikimedia, via Science Friday

THE VICAR, IN THE PUB, WITH THE NICOTINE?:

[Nicotine] is more familiar to us as the addictive quality of cigarettes and tobacco, but if you have too much of anything it will kill you. And too much nicotine is about a gram, possibly less, which is a very small amount. Mercifully for the vicar, it’s a very fast acting poison, so that was undoubtedly unpleasant for him. It was a short time he had to suffer.

Nicotine, if you’re thinking of using it, you’re going to have to disguise the flavor, because it has a very strong taste of tobacco. But of course he’s English, he’s a vicar, he can’t possibly show his disgust. From a poisons point of view, the British social-crippling attitude of “not making a fuss” is an absolute boon, because we will just swallow down anything, just to not look embarrassed or show ourselves up, so he determinedly swallows down this drink which he doesn’t like, and it’s the end of him.


SETTING UP THE FIRST NOVEL

The Mysterious Affair at Styles starts off — you’ve got this big country house, very stereotypical setting for Christie. You have a wealthy older relative, you have a younger generation that are short of cash, desperate for their inheritance — and just to make sure that this older relative’s time is limited — she just married a much younger man and everyone’s worried that their inheritance is going to go to the husband rather then to them. There are many possible suspects in this particular setup, so it’s very unsurprising when Mrs. Inglethrop is found in the throes of horrific convulsions one morning.


IN WHICH SCIENCE FRIDAY PLAYS A CLIP OF DETECTIVE POIROT, AND KATHRYN DESCRIBES HIS THEORY THOROUGHLY [audio]:

It’s a setup of three drugs in combination, so Christie really went to town on her knowledge of drugs. The strychnine would have been prescribed to little old ladies to perk up their nerves, and oh boy will it perk up your nerves! You would have about a lethal dose, dissolved up in a bottle, but you would only have a spoonful a day — so you would never get a lethal dose. But the addition of bromide powders, which were prescribed as sleeping powders or a sedative, if you combine the two as Detective Poirot points out, all of the drug sinks to the bottom of the bottle and you potentially get this lethal dose in the final spoonful. And this is absolutely accurate. There is a book that Christie very likely studied for her exams, called The Art of Dispensing, and it describes this exact setup — as a warning to dispensers not to combine the two drugs because this happened in a real life case. A lady died because she swallowed a lethal dose in her final spoonful of medicine. So Christie had a ready-made plot from her research days when she was studying for her exams.


HOW CHRISTIE SAVED LIVES WITH HER POISON PEN

Her descriptions of poisoning are so accurate, particularly the more unusual poisons — there was a case in both South America and in the UK — that people, because they had been reading The Pale Horse, recognized the symptoms of thallium poisoning and were able to get doctors to intervene, administer antidotes, and save these people’s lives.


This article originally appeared in audio form on Science Friday (9/25/15)


Kathryn Harkup read 83 Agatha Christie novels for research on her latest book, A IS FOR ARSENIC — available now wherever books are sold!

Amazon | Barnes & Noble | Indiebound | Powell’s


Kathryn Harkup is a chemist with extensive knowledge of poisons and a passion for Agatha Christie’s mysteries. She is a freelance science communicator who delivers talks and workshops on the quirky side of science. This is her first book.

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