'Mistaking Cause for Effect, 1849'.

'Mistaking Cause for Effect, 1849'. A boy thinks the Water Board man is turning on cholera. Cholera first appeared in Britain in 1831, and outbreaks occurred regularly in London in the mid 19th century. Its relationship with contaminated water was not understood until established by John Snow (1813-1858). Snow published his theory in a pamphlet in 1849, but did not prove his findings to be correct until another epidemic occurred in 1854. From Punch, London, 1849. (Photo by Ann Ronan Pictures/Print Collector/Getty Images)