Foxglove, also known as dead man’s bells and witch’s glove, is a tall biennial whose tubular flowers are built for long-tongued bees and whose every part is poisonous. Leonhart Fuchs named the genus Digitalis in 1542 after the German word for thimble, and the English name comes from the Old English for fox’s glove, not from the fairy folk later Victorian writers proposed. In 1652 Nicholas Culpeper recommended it in The English Physician for wounds, epilepsy and the King’s Evil, uses the episode notes have no evidence behind them, and herbalists largely abandoned it because doses were so unpredictable.

In 1785 William Withering published An Account of the Foxglove after picking it out of a Shropshire woman’s 20-ingredient remedy for dropsy and spending 10 years adjusting doses. The hosts explain how its cardiac glycosides inhibit the sodium potassium pump, flood heart cells with calcium and make a failing heart squeeze harder. They also cover the dangers of an overdose, the art history theory linking it to Vincent van Gogh, and the plant’s new role in genetics labs.

• Why the gap between a helpful dose and a toxic one is so narrow
• Digitalis toxicity, from vomiting and dangerous heart rhythms to halos and yellow-tinted vision
• The 1981 theory that foxglove explains Van Gogh’s yellow period, and why letters and medical records point to a myth
• Why shocking a poisoned heart is generally avoided, and how the antibody antidote known as Digibind works
• Digoxigenin, or DIG, used today as a molecular probe that lights up DNA and RNA sequences