Driving you hairless

William Crookes named thallium after the bright green colour it produced when its salts were put into a Bunsen burner flame. He compared the colour to that of a fresh green shoot, so he based its name on the Greek word for this, which is thallos. Thallium’s deadly nature was not at first appreciated and it became part of the treatment for ringworm of the scalp, given in relatively large doses to children because it caused their hair to fall out, the better to treat the disease. Meanwhile others were using it to kill vermin, and always thallium brought tragedy in its wake. Agatha Christie built one of her murder mysteries around thallium poisoning. In 1952 she wrote The Pale Horse, in which the murderer used it to dispose of people’s unwanted relatives and disguised his activities as black magic curses. The plot involves a murdered priest and a pub owned by three modern-day witches. Christie described the symptoms of thallium poisoning very well: lethargy, tingling, numbness of the hands and feet, blackouts, slurred speech, insomnia, and general debility, and she is sometimes blamed for bringing this poison to the attention of would-be poisoners. However, her book was responsible for saving the life of one young girl as we shall see. In any case Christie was not the first mystery writer to employ this deadly agent. In Final Curtain, written in 1947, the novelist Ngaio Marsh had her villain using it. The murder to be investigated was the death of Sir Henry Ancred who had been poisoned with thallium acetate which had been prescribed in the treatment of his granddaughter’s ringworm. Marsh clearly had no knowledge of how thallium worked in that she imagined that those poisoned with it would drop dead in minutes. Would-be murderers seeking to emulate her villain would have been very puzzled when their intended victims appeared to suffer no ill effects, although this disappointment might only have lasted a few days, and then they would have been fascinated at the many symptoms it produced.