Cholera, Chloroform, and the Science of Medicine: A Life of John Snow (review)

Three physicians of different specialties, a European historian (team leader), an American historian, and a geographer have produced a landmark book. John Snow is analyzed as a scientist, a theorist, and a physician, developing the scientific foundation for inhalation anesthesia and proving the method of transmission of cholera.

Born in 1813, eldest child of a laborer, Snow began his medical education at fourteen as an apothecary. He came to London in 1836, walked the wards, attended lectures, and was caught up in the enthusiasm for the application of chemistry to medicine. He began as a general practitioner and slowly improved his medical credentials. In 1846 he observed the use of ether, did clinical studies and animal experiments, described dose ranges and an apparatus for administration, and published a seminal text on the Inhalation of Ether in 1847. Adopting chloroform, he anesthetized surgical and obstetrical patients. He measured blood gases, tested various agents, continued animal experiments in his home laboratory, and built a solid anesthesiology practice of more than five hundred cases a year, twice giving chloroform to Queen Victoria in childbirth. He noted how anesthesia permitted a marked expansion in the number and kind of operations.

Snow is best known for his cholera research. This book offers a close-grained analysis, with new insights and new data. The prevailing theories of cholera transmission are dissected and compared to Snow's theory of a water-borne fecal-oral route of a "cholera poison." Proper emphasis is given to his deductions from the gastrointestinal symptoms. His studies of Thames River water supplies and cholera deaths supported his ideas, which were presented in On the Mode of Communication of Cholera in 1849. The profession did not agree. Cholera returned in 1853, and Snow studied cholera deaths from two Thames River water companies supplying identical populations, one source contaminated with sewage. The data were essentially unequivocal, although not easy to collect or analyze: drinking Thames sewage caused cholera. There is a detailed and useful epidemiologic analysis of this study, discussing its problems and pitfalls. The well-known Broad Street Pump outbreak, a point-source epidemic of "upwards of 500 cases"¹ occurred in September 1854; the "interview with the Board of Guardians . . . on Thursday, 7^th September"² and the pump-handle removal are well-known tales.

As the authors make clear, the proof of water transmission was for Snow the water companies study, the Broad Street work only confirmatory. The data in the 1855 pamphlet on the "communication of cholera" were refined and better reported in the seldom-cited 1855 Cholera Inquiry Committee Report to the Vestry of St. James Parish. The two reports are carefully compared, emphasizing Henry Whitehead's extensive data collection and his important discovery of the index case and a cesspool leak into the pump well. The Board of Health ruled that filth and miasmas caused the outbreak.

A new and important contribution is a detailed discussion of Snow's maps, especially the spot maps of the Broad Street data. The authors make clear that the spot map did not drive his theory—it was an illustration for his narrative. There is a useful table of various maps of cholera spread, distribution, and occurrence. The Broad Street maps became ubiquitous and were altered, misrepresented, distorted, and used to further the cause of computer-based geographic information system technology. A family tree of Snow maps has twenty-seven descendants.

A brief discussion of the sanitary movement is well done, to include Snow's parliamentary testimony rebutting the "bad odor" miasma theories and his rejection of the "filthy habits" of the poor as causes of diseases. His 1853 oration on "continuous molecular charge" presents Snow's view that living systems have common properties and linked chemical and physiological interactions. He used his anesthesia data and...