"had their gums and toes painted with gentian violet solution"

Gentian violet, technical name hexamethyl pararosanaline chloride, is a blue-violet medical dye that has antibacterial and antifungal properties, as well as some effectiveness in driving parasitic worms from the body. It is commonly used to mark the skin for surgery preparation and allergy testing, and to treat Athlete’s foot, ringworm, mouth ulcers, impetigo, and abrasions.

It was first synthesized in 1861. The name refers strictly to its color; it is not made from either the large genus of gentian flowers or from violets. Although still listed by the World Health Organization, its applications have mostly been superseded by more recent drugs.