He was thin and weak, and his voice was almost inaudible despite the relative quiet of a teaching hospital side room. By the time I joined the firm as a student, he had endured a fever of unknown origin for over a month. Allocating him to me, the house officer had explained that his hairy cell leukaemia should be curable were it not that the source of his fever remained stubbornly elusive. Instead, he lay drained, submitting to repeated blood cultures and increasingly invasive investigations.

After retiring as a schoolmaster, he had trained as a missionary and travelled widely. All manner of latent exotic infections might be coming back to haunt him, but all the test results were negative. Finding a good vein for the blood …