On the cause of offence

Abstract

We continue our celebration of the Snow bicentenary in this issue of the IJE by reprinting John Snow’s paper ‘On the supposed influence of offensive trades on mortality’ originally published in the Lancet in 1856. Of the pieces included in the celebration this is the only one actually written by Snow himself. In 1855 Snow had stirred up controversy and opprobrium, in particular from Thomas Wakley, founder and editor of the Lancet, when he appeared as an expert witness in front of the parliamentary committee assessing the proposed Public Health and Nuisances Removal bills. Snow’s main argument was this: if the offensive trades were indeed harmful to the public health, rates of disease and death among those who worked in them would be high and, as far as he had been able to learn, this was not the case. In his commentary, David Lilienfeld speculates on Snow’s reasons for publishing the paper. Was it a response to Wakley’s stinging attacks the year before? As Jan Vandenbroucke points out, the arguments as presented by Snow to the parliamentary committee do indeed come across as somewhat dogmatic. Maybe this was Snow’s attempt to justify that dogmatism. We will never know for sure. Certainly Snow’s oral-faecal theory of the transmission of cholera proved to be correct; his assumption that the oral-faecal theory would apply to all infectious diseases did not. Wakley’s jibes at members of what he jeeringly calls the ‘Offensive Trades Association’ or the ‘Offensive Association’, ’These unsavoury persons, trembling for the conservation of their right to fatten upon the injury of their neighbours’, display a deep contempt. However, his most vitriolic comments are reserved for Snow. In his own time, Snow was best known for his contribution to anaesthesia. His deep understanding of the diffusion of gases combined with his own theory that cholera was transmitted by the oralfaecal route made it impossible for him to accept the dominant theory that epidemic diseases were caused by miasmas emanating from decaying animal or vegetable matter and spread through the atmosphere. In his editorial attack, reprinted as a Diversion in the current issue of IJE, it seems to be Snow’s refutation of this dominant paradigm that most infuriates Wakley as he targets Snow’s lack of scientific evidence and dogmatism. However, Wakley himself makes a poor case for the miasma theory, his evidence resting on his own observation that ‘failing strength, flabby muscles, pallid cheeks, lassitude of body, and torpidity of mind’ are most frequently the result of noxious gases from leaking drains, and on his assertion that ‘there is hardly a practitioner of experience and average powers of observation who does not daily observe the same thing’. More considered criticism of Snow’s paper can be found in the other Diversion in this issue: a letter to the Lancet by John Tripe, who had been appointed Medical Officer of Health for Hackney in London the year before. Tripe takes issue with Snow on two counts; one is the denominator he uses, which is based on the 1851 census and does not allow for population growth, and the other continues the debate, initiated by Snow, on what we now know as the healthy worker effect. Snow uses the lower mortality rate among workers in the offensive trades to argue against their detrimental effect on health. Careful to state that his comments are in no way intended to denigrate Snow’s work, Tripe argues the case for reverse causality; that people can only engage in the physically demanding work of the offensive trades while they are fit enough and leave to swell the mortality rates of other trades when they are not. Tripe was an active Fellow of the Royal Meteorological Society from 1856 until his death and the Society’s President in 1871. His obituary lauds his contribution to the relationship between meteorology and health, disease and death. However, it seems that Tripe was far from a confirmed miasmatist. During discussion of a paper in the society’s Quarterly Journal, Tripe is reported as stating ‘that the spreading of the disease [cholera] does not always arise from atmospheric conditions, but that to a great extent it spreads from person to person.’ It would be easy to dismiss Wakley merely as an editor who misused his position to vent his spleen on those whose views he held in contempt. Snow’s obituary in the Lancet on the 26 June 1858 was shockingly brief. Devoid of any mention of his work on the transmission of cholera, the Lancet in April 2013 felt the need ‘after an unduly prolonged period of reflection’ to correct the perception that it may have Published by Oxford University Press on behalf of the International Epidemiological Association