Last week, I wrote about scientists who developed a stool substitute and used it to cure gut infections in two women. This sham poo contained 33 gut bacteria, which were meant to displace the harmful ones that were causing diarrhoea in the patients.

For decades, doctors have been doing the same thing using actual faeces. This unorthodox technique, known as a faecal transplant, has been used to treat over 500 people with recurring infections of the diarrhoea-causing bacterium Clostridium difficile.

The concept is inherently revolting, and many mistake it for pseudoscience. But faecal transplants work. Over 90 percent of patients make a full recovery, far greater than the proportion who responds to conventional antibiotics. (In fact, it may be antibiotics that cause