American Scientist

A IS FOR ARSENIC: The Poisons of Agatha Christie. Kathryn Harkup. 318 pp. Bloomsbury, 2015. $27.00.

As much as I love my chosen field of toxicology, I don’t often turn to it as a topic for leisure reading. All too often toxicology texts can be dry and fact-dense. But sometimes I make exceptions. When I came across a book focusing on toxicological analysis of poisons used in Agatha Christie’s murder mysteries, I was intrigued. When I saw that the book opens with a quote from Shakespeare, my curiosity was further piqued. And when I found that the author is both a toxicologist and a fine storyteller, I realized that reading A Is for Arsenic would be a win-win.

Author Kathryn Harkup, who holds a PhD in chemistry and has focused her research on phosphines, first explores Christie’s life and explains why she was uniquely qualified to write murder mysteries. The bestselling author, it turns out, had been an apothecary’s assistant during World War I. Because of her experience in the pharmacy, Harkup explains, she had an excellent understanding of compounds that could be used to either aid or harm, depending on the precise mixture and dose. Harkup also confesses her affection for Christie’s work. Rather than following the time-worn academic path of distancing herself from her subject as a display of objectivity, Harkup is open about her status as a Christie fan. It is a badge she wears with pride, and her affection for the books she discusses adds considerable warmth.

As the book’s title implies, Harkup organizes the book alphabetically according to the poisons Christie uses in her novels. Chapter 2 is titled “B is for Belladonna”; chapter 3, “C is for Cyanide”; and so forth. Harkup introduces each poison by describing how it is used, both legally and illegally, and how Christie introduces it into her novels. She then discusses how the poison acts on the body and explains its history and origin, describing how it was discovered. For me, as a toxicologist, these latter details are of particular interest, because my work tends to focus strictly on the poison itself. Instead of merely noting that “belladonna is the common name for nightshade, which is toxic due to the presence of Atropine”—information easily found in a toxicology textbook—and moving on, Harkup discusses the name’s origin in Greek mythology, then goes on to explore belladonna’s appearance in other literature, from the Bible to Shakespeare’s plays to the Harry Potter series.

Harkup walks a fine and tricky line: She sidesteps potentially snooze-inducing scientific minutia while also managing to avoid dumbing down her topic. For instance, when she discusses the molecular actions of cyanide, she concisely describes what the compound targets in the cell and explains why that part of the cell is essential for its survival. She doesn’t go into the molecular mechanisms of inhibition that result from irreversible binding to cytochrome c oxidase, which halts the oxidative phosphorylation chain (zzzzz…); nor does she state that cyanide is bad because a cell exposed to it cannot “breathe” (a common oversimplification). She explains that cyanide can bind to hemoglobin because of its physical similarity to iron, noting that this similarity allows cyanide to bind to an enzyme in the adenosine triphosphate production chain that also binds iron. Because cyanide can inhibit this enzyme, which is involved in energy production, the cell cannot function.

Interweaving an account of the scientific importance of a compound with some discussion of its historical implications proves a fascinating approach. Harkup gives readers an expansive view of each toxin—explaining, for example, how a poison changed merchants’ trade routes, affected military science funding during World War I, or presented obstacles to scientists endeavoring to prove that a victim had succumbed to its effects. In her chapter on hemlock, Harkup tells of Socrates’s execution, going beyond the familiar parts of the tale. Unwilling to toe the political line, the philosopher ran afoul of the Athenian government and was condemned to death in 399 BCE. His jailer, Harkup explains, was familiar enough with using hemlock for executions that he warned Socrates not to talk after drinking the poisoned cup, because doing so would interfere with the toxin’s action. That, in turn, would require the jailer to mix and administer another dose. “Socrates appears to have been indignant” about the order to stop talking, she says. “He told the jailer that he should be prepared to give him poison two or three times.”

Finally, in each chapter Harkup guides the reader through plots from Christie’s novels that feature the selected poison, describing how the victim’s symptoms and death affect the plotline. Often she compares the fictional murders with historical poisonings or demonstrates how the symptoms described in the novel correlate with the pathological effects of toxic exposure related earlier in the chapter. In “O is for Opium,” Harkup discusses the novel Sad Cypress , which presents a case in which Hercule Poirot, Christie’s famously fastidious Belgian detective, must deduce how the poison was introduced to the victim—a task complicated by the fact that the toxin might have been consumed during a meal shared by two others who were asymptomatic. Poirot notices a pin-prick mark on the wrist of one of the other diners. This could indicate a potential means of introducing an antidote into her system, or it could simply be a mark from a rose thorn, as the diner claims. By comparing the effects of injected and ingested opium, he determines how the crime was committed and whether the diner was telling the truth.

Perhaps most important, Harkup carefully warns her readers before discussing a novel’s ending. Those who skip the spoilers will find that Harkup’s background discussions of the poisons actually ratchet up the tension as she revisits certain details in the books. Readers may find themselves digging up Christie novels they haven’t perused to learn the identity of the poisoners—meanwhile enjoying another great read.