FOR centuries, doctors have been urging patients to watch out for unhealthy
bleeding—in their stools, urine or saliva. Blood in these can be a sign of
anything from cancer to tuberculosis, and patients are told to report it
promptly. But what if they suffer from red-green colour blindness, a common
hereditary condition?
Gary Wormser and his colleagues from New York Medical College showed
colour-blind people colour photos of samples with and without blood in them
(Archives of Internal Medicine, vol 161, p 461). The colour-blind
subjects were much worse at recognising blood than people who could distinguish
colours,…
