He became interested in two theories that possibly explained how
cholera killed people. The first suggested that cholera multiplied
in the air. A cloud of dangerous gas floated around until it found
its victims. The second suggested that people absorbed this disease
into their bodies with their meals. From the stomach the disease
quickly attacked the body and soon the affected person died. John
Snow suspected that the second theory was correct but he needed
evidence. So when another outbreak hit London in 1854, he was ready
to begin his enquiry. As the disease spread quickly through poor
neighbourhoods, he began to gather information. In two particular
streets, the cholera outbreak was so severe that more than 500
people died in ten days. He was determined to find out why.