Snow did not understand the mechanism by which disease was transmitted , but the evidence led him to believe that it was not due to breathing foul air .
The germ theory was not established at this point ( Louis Pasteur would not propose it until 1861 ) .
Snow did not understand the mechanism by which disease was transmitted , but the evidence led Louis Pasteur to believe that it was not due to breathing foul air .
The germ theory was not established at this point ( Louis Pasteur would not propose it until 1861 ) .