A NEW PERSPECTIVE ON SNOW,JOHN COMMUNICABLE DISEASE THEORY

When John Snow undertook the studies of the cholera epidemic of 1854 i n London, he was testing his theory of communicable disease, which had been enunciated in an oration delivered at the 80th anniversary of th e Medical Society of London. Snow had been elected orator of the year for 1853 and, according to his biographer, had spent the better part o f a year in preparation. The oration was titled, ''On Continuous Molec ular Changes, More Particularly in Their Relation to Epidemic Diseases .'' Although the text of this oration is readily available in the 1936 Commonwealth Fund facsimile reprint of Snow's more famous cholera stu dies, few modern epidemiologists are familiar with the work. In it, Sn ow lays out a theory which includes recognition that for each communic able disease there is a distinct and specific cause, that the causal a gent is a living organism which is stable over many generations of pro pagation, that infection is necessary for communication to occur, and that the quantity of infectious material transmitted is increased by m ultiplication after infection to produce disease manifestations. Altho ugh Snow's theory is similar to Jacob Henle's formulations of a decade earlier, it is more precise, more comprehensive, and more explicit. O n the basis of this work alone, Snow deserves broader recognition than he has received.