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I realise that “rubbing salt into the wound” was a way of preventing infection. But how did it work?

• Blood is 83 per cent water. Because salt is hygroscopic, it absorbs water, accelerating the tendency for blood to clot and drying the wound. This helps deny microorganisms a favourable habitat. Saline also generates osmotic pressure – it forces water out of microorganisms to equalise the salt concentration across their cell membranes. This can kill them, so salt acts as a disinfectant.

The stinging of the wound signals that salt does cause injury to the body. But in the absence of a better option at the time, killing a few healthy skin cells was acceptable collateral damage when the alternative may have been infection and possibly death.

Mike Follows, Willenhall, West Midlands, UK