This paper presents a commentary on the testimony delivered by Dr. John Snow before the British Parliamentary Committee in 1855. It is noted that in Snow's testimony was highlighted his extremely strong belief in germ theory and contagion and his consequent contempt for anything close to the rivaling theory that miasmatic emanations cause disease. Snow's unreasonableness may have been because he already held his germ theory and drinking water convictions before he made his observations. In addition, based on his published books it has become apparent that even his data analysis was guided by such preconceptions. Although Snow's opinion on germ theory created contemporaries, it is noted however, that Snow did not truly sway contemporary opinion, and his theories were not agreed as a complete breakthrough in the way that they are often presented as being in epidemiological textbooks. Overall, the fundamental problem with the miasma and contagion theories at the time was that both failed to answer certain questions, including transmission of diseases, development of diseases, and the issue of temporary carriers of causative germs.
Vandenbroucke, J. P. (2000, July 1). Invited commentary: The testimony of Dr. Snow. American Journal of Epidemiology. https://doi.org/10.1093/aje/152.1.10