The Rules of Contagion

ale and imported water, who didn’t get sick. Then there was
Susannah Eley and her niece, who had their water shipped from
Soho to Hampstead and fell ill. As the outbreak grew, Snow decided it
was time to intervene. Public health in Soho fell under the
responsibility of a local Board of Guardians. He turned up uninvited at
one of their meetings and presented his arguments. The board didn’t
fully believe his explanation, but decided to remove the pump handle
all the same. The outbreak ended soon afterward.
Three months later, Snow wrote up his theory in more detail. The
report included what would become his most famous illustration: a
map of Soho, with black rectangles showing each of the cholera
cases. The cases clustered around Broad Street, near the pump. It
was a pioneering work of abstraction, removing unnecessary details
and diversions. Whereas abstract artists like Malevich and Mondrian
would later paint blocks of colour to shun reality, Snow’s shapes
brought cholera into focus.[5] His rectangles made a previously
invisible truth – the source of infection – tangible.