"I have enough papers in my drawers to cover Australia," Florence Nightingale wrote to a friend in 1895 when she was in her mid-seventies. Aside from reinforcing a sense of the sexual innuendo that has adhered to Nightingale's name ever since Lytton Strachey's portrayal of her in Eminent Victorians, this statement throws down a challenge to anyone with the temerity to attempt to write about her. It also conceals an in-built trap, namely that the weight of documentary material combined with the length of her lifespan - she lived to the age of 90 - often makes it extremely difficult to speak of many aspects of Nightingale's life and career with a reasonable degree of certainty.

Oblivious to this problem, the bacteriologist Hugh Pennington recently tumbled headlong into the trap. Initially, in an article in the London Review of Books, and then subsequently on Radio Four's Today programme, he claimed, with mounting insistence, that Florence Nightingale must be accounted a bad nurse because she never believed in germ theory. In Pennington's version, to the end of her days, Nightingale continued to assert a miasmatic theory of disease transmission according to which certain airborne poisons, or miasmata, when inhaled into the lungs, generate fever. And she is said to have stuck to this belief, despite all the scientific evidence confirming that germs cause disease, which began to emerge from laboratories in the late 1870s.

In fact, Nightingale began to change her mind about the existence of germs at roughly the same time that other members of the medical establishment were doing so. Robert Koch's identification of the cholera bacillus in 1883 appears to have been the crucial breakthrough for her. By the beginning of the 1890s, Nightingale was advocating slide lectures showing germs swimming about in polluted water for village communities in rural India.