In the course of her career, Agatha Christie killed hundreds of characters: some by drowning, some by stabbing, and one with a crowbar. But her preferred murder weapon was chemical, rather than physical. “Give me a decent bottle of poison,” she is supposed to have said, “and I’ll construct the perfect crime.”

Or, perhaps, the perfect murder mystery: as Kathryn Harkup demonstrates, inadvertently, in a new book, “A is for Arsenic: The Poisons of Agatha Christie,” Christie’s fictions are profoundly shaped by the poisons that their characters skillfully employ. What’s more, those characters enjoy relatively unfettered access to a range of exotic toxins, in a way that a would-be murderer could only dream of today. One begins to suspect that, among the many factors that gave us Christie’s enormously popular novels, we must count the particular period for poisoning in which she lived.

Harkup is a chemist, as well as a Christie fan. Christie, she writes, “freely admitted to knowing nothing about ballistics,” but used poisons “with a high degree of accuracy.” Christie also used them far more frequently than any of her contemporaries. Her meticulous use of strychnine was even remarked upon in a review in the Pharmaceutical Journal, much to Christie’s delight.

Her expertise can be traced back to volunteer service in the local hospital dispensary during the First World War, during which time Christie trained as an apothecary’s assistant. She successfully passed her exams in 1917, after receiving private tuition from a local commercial pharmacist. Mr. P., as she referred to him, was a rather alarming character, whom Christie caught making a potentially fatal mistake while formulating suppositories, and who carried a lump of curare in his pocket at all times, because, he said, “it makes me feel powerful.”

Mr. P. went on to play a starring role in one of Christie’s later mysteries, “The Pale Horse,” and Christie’s firsthand experience in the delicate art of handling potentially deadly drugs became central to her books. In Christie’s fictional universe, as Joan Acocella has written for this magazine, emotional depth is forgone in favor of elaborate and entertaining puzzles. After all, as Acocella points out, “if she had given her characters any psychological definition, we could have solved the mystery,” and the addictive quality of Christie’s whodunit formula would have suffered as a result. The cold, calculating nature of murder by poisoning, as opposed to the violent passion implicit in a stabbing or strangulation, is precisely suited to propelling plots in which any one of the characters could be the culprit, all the way until the very end. In many ways, the poison was the personality in Christie’s stories—the element of surprise amid an otherwise reassuring collection of country-house clichés.

According to Harkup, when it came to poisons, “Christie invariably played with a straight bat”: no untraceable poisons, no implausible sourcing, and just three invented drugs, only one of which was used to kill. Harkup plays it equally straight, sticking to her own formula so closely as to risk tedium. After a promising introduction, readers are left to plod through the next fourteen chapters, each of which details, in the same order, the toxicology, availability, famous real-life cases, and Christie’s fictional use of arsenic, strychnine, cyanide, and eleven other poisons. Fortunately, interesting tidbits emerge: digitalis intoxication may have been responsible for van Gogh’s “yellow period”; eating phosphorus-laden match heads was a surprisingly common method of suicide in the nineteen-twenties; and arsenic was popular enough among murderers that its French nickname was poudre de succession, or “inheritance powder.”

More intriguingly, out of the somewhat mind-numbing accumulation of detail, it becomes possible to discern the ways in which chemistry, rather than character, drives Christie’s plots. It is the poison that provides the pacing, for example, in the Hercule Poirot mystery “Five Little Pigs,” in which the time it takes for a lethal dose of hemlock to take effect allows five potential murderers, all of whom have good cause to wish the unlucky Amyas Crale dead, the opportunity to strike. Again and again, the varying availability, symptoms, antidotes, and post-mortem detection methods of particular poisons shape both the actual crimes and Christie’s careful orchestration of red herrings and clues. Arsenic’s solubility in hot water, atropine’s bitter taste, even phosphorus’s propensity to endow its victims’ intestines with an eerie glow, not to mention “smoking-stool syndrome”—in each case, it is the poison’s strengths, weaknesses, and idiosyncrasies that structure the narrative and eventually allow Miss Marple, Poirot, or one of Christie’s other amateur detectives to solve the mystery.

Indeed, as the examples (and dead bodies) mount up, Christie’s rigorous rejection of character and motivation in favor of chemical agency comes to seem almost avant-garde. Meanwhile, as Harkup points out, while she favored cyanide, Christie was frequently esoteric in her choice of poisons. Hemlock, for example, had not been used in an intentional poisoning since Socrates’ day, according to Harkup. Ricin, which is deployed against four members of the same household in “The House of Lurking Death,” had no track record as a murder weapon at the time Agatha Christie was writing, Harkup says, despite being potent, untreatable, and easily consumed accidentally in the form of castor-oil seeds. “In many respects,” Harkup writes, Christie’s use of ricin “was years ahead of her time.” (Ricin had a brief moment of notoriety when the Bulgarian dissident Georgi Markov was assassinated in London using a ricin-tipped umbrella, in 1978, but its current fame is owed mostly to Walter White, of “Breaking Bad,” who favored ricin as a means of disposing of anyone who got in his way.)

What’s most striking about Harkup’s exhaustive descriptions, however, is the portrait they draw of a culture awash in poisons. In early-twentieth-century Britain, patent tonics contained strychnine, opium could be bought over the counter without question, and no gardener’s shed was without a stock of potassium cyanide (for use as an insecticide). Meanwhile, the Industrial Revolution had democratized arsenic: as a byproduct of smelting iron ore, arsenic trioxide was scraped out of chimneys in vast quantities. “Soon,” according to Harkup, “anyone and everyone could afford enough arsenic to dispatch an unwanted relative or inconvenient enemy.” The nineteen-twenties and thirties, when Agatha Christie began her career, are known as the “Golden Age of Detective Fiction,” in which a cohort of mostly British authors defined the standards of the genre. Seen through the lens of Harkup’s research, it seems equally to have been the golden age of poisons, after the first flowering of organic chemistry and before the stricter regulations that arrived after the Second World War. Never before or since, it seems, has the would-be murderer—or murder-mystery writer—been furnished with such a range of easily available toxins.

Indeed, Christie’s attention to detail left her open to the accusation that she offered a handbook for would-be murderers. Harkup recounts a 1977 case in France, in which Roland Roussel, a fifty-eight-year-old office worker, murdered his aunt using atropine eye drops. The gendarme who found a copy of the Miss Marple mystery “The Tuesday Club Murders” in Roussel’s apartment reportedly declared, “I’m not saying Roussel was inspired by the book, but we found it in his apartment with the relevant passages on poison underlined.”

At the same time, Christie’s precision when it came to poisons can apparently be credited with saving at least two lives. Harkup quotes a 1975 letter from a woman in South America who had raised justified suspicion that an acquaintance was being poisoned by his young wife: she wrote to Christie in thanks, concluding, “but of this I am quite, quite sure—had I not read ‘The Pale Horse’ and thus learned of the effects of thallium poisoning, X would not have survived.” Two years later, soon after Christie’s own death, a nurse with a taste for mysteries spotted the symptoms of thallium poisoning in a nineteen-month-old in Qatar. In their report, the child’s physicians acknowledged their indebtedness “to the late Agatha Christie for excellent and perceptive clinical descriptions, and to Nurse Maitland for keeping us up to date with the literature.”