Most physicians continued to rely on miasmatic theory. According to this theory, which came from ancient times, the miasmas, which in Greek is pollution, produced a series of diseases, that is, smelly emanations of soiled lands and waters. Others began to defend Louis Pasteur's new microbial theory. The latter included John Snow (1813-1858). Born within a family of peasants, the cholera that spread among the Killingsworth mining coal in his youth witnessed a terrible plague that led him to fight the disease and study medicine for it.

In that 1848 cholera outbreak, Snow used an innovative method. He did not visit the sick at home, placed the cases on a map and concluded that most of the sick and dead concentrated around public or private water pumps. It was the first time that the geographic method was used to study an epidemic. The following year he founded the pioneering London Epidemiological Society with other doctors.

In 1854, another outbreak of cholera allowed him to continue the investigation. In the Soho neighborhood, half a kilometer in diameter around Broad Street, it caused more than 700 deaths in a single week. He took a map of Soho and, with the help of the parish priest and the archive of the Middlesex hospital, he placed all the deaths in September. He found that the epicenter of all the points on the map and, therefore, the origin of the outbreak was the Broad Street public bomb. He got the authorities to close the bomb and the plague stopped immediately.

Years later, members of the London Health Council decided to re-believe in the myasthmatic theory because they were unwilling to invest to ensure the water supply in Soho. The Broad Street bomb was reused and cholera came back stronger than ever to Sohora. Even though John Snow was already dead, hundreds and hundreds of people who caused cholera were right.