Sherlock Holmes and the Case of the Poisonous Plants

In The Adventure of the Devil’s Foot (1910), Holmes investigates the death of a sister and brother that has left their two other brothers insane. Holmes deduces they were killed by a West African plant poison that affects the brain.

The poison is never explicitly named but its description matches the Calabar bean.

In southeastern Nigeria, known then as Old Calabar, the bean was used in witchcraft trials. If the accused person survived ingesting the poison, they were considered innocent. But by the 1880s, English doctors used it to treat glaucoma.

Doyle owned a similar book, titled The Essentials of Materia Medica and Therapeutics. His copy has been preserved and digitized by the Harry Ransom Center at the University of Texas at Austin.

Doyle’s marginalia reflect his obsession with poison. Some pages have handwritten notes about the effects of drugs on human bodies. Doyle filled this page with playful poems about opium and tartar emetic.

Since the 1600s, opium from India was used in English medicines like laudanum. By 1803 pharmacists had learned to extract morphine from opium masses and believed they had tamed its addictive side. But they hadn’t.

While some in England became addicted to opium, the British Empire also used the plant as a tool of colonial control. The British cemented their economic presence by smuggling opium into China and giving samples to local people.

This had catastrophic effects on Chinese society as many became dependent on British opium.

Today’s pharmacists conjure up pictures of people counting pills made by corporations in faraway factories, like in this image. But until the mid 1800s, most drugs were created straight from plants one batch at a time. 

Local pharmacists, called apothecaries back then, worked directly with botanical materials, creating the foundation for the present-day pharmaceutical industry.

In The Sign of the Four (1890), Holmes and Watson investigate the murder of a man guarding a hidden treasure taken from India by his father, a guard in the Andaman penal colony. 

They discover he was killed by a blow dart coated in a strychnine-like poison, shot by an Andamanese Indian assistant to a former British officer.

The strychnine tree is indigenous to India, Sri Lanka, and Indonesia. People there used its seeds for centuries as a neurological, sexual, and digestive stimulant. 

As trade between Europe and Asia expanded in the 17th century, strychnine became a popular household rat poison in England. By the Victorian period, physicians were studying its medicinal properties.