Many of the medical problems (Chapter 11) which seafarers contracted in the early to mid-nineteenth century would now be considered infective in origin, but it was not until the late nineteenth century that this was seriously considered to be the case. In the early days of the hospital-ships, the sole illness considered to be contagious and a danger to immediate contacts, was smallpox; the remainder, it was felt, were caused by ‘miasmas’. Although John Snow (1813–58) had demonstrated, on epidemiological grounds, that cholera was water-borne (in the 1853–4 outbreak in London), this was not widely accepted until very late in the century. Tuberculosis (see Chapter 23) (which was of major importance in seafarers) was also not considered an infectious disease until at least, the mid-nineteenth century. Smallpox (variola) was of course readily identifiable on clinical grounds. 1