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"Snow on Cholera . . . together with a biographical memoir by B. W. Richardson and an Introduction by Wade Hampton Frost."

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(1936)Cambridge, MA: Harvard University Press, 1936. Reprinted by Hafner, 1965. Contains reprints of MCC2, CMC, and Snow's 1856 response to Simon's report on cholera in South London

PDF from photocopy; Michigan State University Libraries.

The PDF contains front matter, the introduction and appendix by Frost, and the list of Snow's principal writings. The table of contents of the book is as follows:



John Snow, M. D., a representative of medical science and art of the Victorian era, by B. W. Richardson. [Frost and the publication committee selected the abbreviated version of Richardson's biographical sketch from The Asclepiad (1887).]

On the Mode of Communication of Cholera (1855). [page numbering is identical with the original.]

On Continuous Molecular Changes (1853).


1. Cholera and the water supply: later papers. [Frost's discussion of Snow's October 1856 article, "Cholera and the water supply in the south districts of London in 1854," a response to John Simon's Report on the last two cholera-epidemics of London as affected by the consumption of impure water (May 1856).]

2. The principal writings of John Snow, M. D. [The list of writings is understandably incomplete and contains some inaccuracies. For a current list, see the index page to Snow's publications (chronological) on this web site.]

PVJ's review of Frost's introduction

Uncertainty in epidemiology is the norm, states Frost. Since epidemiologists often find themselves in confusing situations where multiple theoretical explanations are proposed, he believes that we can learn by studying those who, in parallel epidemiological situations in the past, got it right. Snow is "a nearly perfect model" of such a case-study method, for his analysis of cholera epidemics "led him to the confident conclusion that the specific cause of the disease was a parasitic micro-organism, conforming in all essentials of its natural history to what is now known of the Vibrio cholerae" (ix). Later, Frost elaborates on this assertion: "Snow's conception [was] that cholera was due to a specific micro-organism, an obligate parasite, propagated only in the human intestinal tract and disseminated by ingestion of excreta . . ." (xvi-xvii).

Both statements are incorrect, as a simple word search of Snow's works on this web site, including the two reprinted papers, easily shows. In the Document Search function on the main menu, type "parasite" and "parasitic" into the keywords box: Snow never used either word in his published writings. Next try "animalcule," the mid-Victorian equivalent to micro-organism; the hits include both editions of On the Mode of Communication of Cholera. Click on the 1849 edition, then Edit → Find, and type animalcule. You will find the following sentence by Snow: "The writer, however, does not wish to be misunderstood as making this comparison so closely as to imply that cholera depends on veritable animals, or even animalcules, but rather to appeal to that general tendency to the continuity of molecular changes, by which combustion, putrefaction, fermentation, and the various processes in organized beings, are kept up" (9). His second use (27) of the term is analogical. While we come up short on a usage that matches Frost's, we see why he and the publication committee decided to couple the relatively unknown oration from 1853, On continuous molecular changes, with the second edition of Mode of Communication.

Back-clicking the browser should bring up the initial result of your Document Search; click on this 1855 edition and look again for animalcule. The first usage is Snow's description of a sample of water taken from the pump in Broad Street: "The water at the time of the cholera contained impurities of an organic nature, in the form of minute whitish flocculi visible on close inspection to the naked eve, as I before stated. Dr. Hassall, who was good enough to examine some of this water with the microscope, informed me that these particles had no organised structure, and that he thought they probably resulted from decomposition of other matter. He found a great number of very minute oval animalcules in the water, which are of no importance, except as an additional proof that the water contained organic matter on which they lived" (52). Some have wondered if these oval animalcules were Vibrio cholerae after all; but it matters little since they went unrecognized at the time. Click on the next usage of animalcule: "As regards the morbid matter of cholera, many other circumstances, besides the quantity of it which is present in a river at different periods of the epidemic, must influence the chances of its being swallowed, such as its remaining in a butt or other vessel till it is decomposed or devoured by animalcules, or its merely settling to the bottom and remaining there. In the case of the pump-well in Broad Street, Golden Square, if the cholera-poison was contained in the minute whitish flocculi, visible on close inspection to the naked eye, some persons might drink of the water without taking any, as they soon settled to the bottom of the vessel" (113).

Back-click the browser to return to your Document Search list, and click on the Report on the Broad Street outbreak by the Parish Cholera Inquiry Committee, search for animalcules, and the single result is: "Unfortunately no microscopic examination of the water was made earlier than September 3rd. On that day it was found by Dr. Snow to contain minute whitish flocculi, described by Dr. Hassall as destitute of organisation; it also contained some oval animalcules, but no portions of digested food are mentioned" (92).

In short, both Hassall and Snow assumed that the micro-organisms they could detect microscopically in potable water were harmless critters feeding on organic matter, not agents of the cholera poison. They were looking for something else: "It would seem that the cholera poison, when reproduced in sufficient quantity, acts as an irritant on the surface of the stomach and intestines, or, what is still more probable, it withdraws fluid from the blood circulating in the capillaries, by a power analogous to that by which the epithelial cells of the various organs abstract the different secretions in the healthy body. For the morbid matter of cholera having the property of reproducing its own kind, must necessarily have some sort of structure, most likely that of a cell" (MCC2, 15).

I find Frost's a-historical mis-attribution of Snow's theory curious. Elsewhere in the introduction, he is accurate, even-handed, and effective in presenting the historical context on the debate amongst competing cholera theorists and the uncertainties they confronted from the first English cholera epidemic in the 1830s until the third epidemic in 1853-54. For example, he mentions the dominance of the pythogenic theory amongst the English, but he takes no cheap shots at these "filth disease" advocates:

"The theories evolved to explain these complex facts [of disease communication] were numerous and diverse, but so far as any one idea was dominant it was probably that expressed by Sutherland as follows:

'It appears as if some organic matter, which constitutes the essence of the epidemic, when brought in contact with other organic matter proceeding from living bodies, or from decomposition, has the power of so changing the condition of the latter as to impress [xii/xiii] it with poisonous qualities of a peculiar kind similar to its own.' To this was added the conception of 'localizing influences' promoting the propagation of the poison, and 'predisposing causes,' increasing susceptibility to its effects" (John Sutherland, Report of the General Board of Health on the epidemic cholera of 1848 and 1849 [1854], Appendix A: 8).

After the Sutherland quote, Frost continued: "To this was added the conception of 'localizing influences' promoting the propagation of the poison, and 'predisposing causes,' increasing susceptibility to its effects. There were many differences of opinion as to whether the 'cholera poison' might be spontaneously generated in different countries, or must be introduced from pre-existing foci; whether it was spread solely by diffusion through the atmosphere or attached itself to solid bodies; whether or not it was communicated by an effluviun (contagion) given off by the sick."

"It is easier, at this distance, to see the defects in the current theories than to do them justice. Some were so vague and general as to be manifestly worthless . . . . But there were at least a few theories, such as Farr's, emphasizing the importance of elevation and drainage, which were well reasoned in accordance with an impressive array of facts. It is perhaps significant that they were directed so largely toward explanation of those phenomena of cholera which are still least explicable: its sudden extensions [xiii/xiv] around the world, the vagaries of its geographic distribution, and its relation to climate, season, and weather."

"How Snow perceived the thread of consistency which connected a seemingly chaotic mass of facts and followed it through to the conclusion that bacteriology has since confirmed, he himself tells plainly and simply, with the fresh enthusiasm of discovery, the restraint of a scientist. His account should be read once as a story of exploration, many times as a lesson in epidemiology."

I cannot resist a critical, editorial comment: if only Wade Hampton Frost had listened to his own suggestion and refrained from telling readers what they would find in Snow's two essays.

Frost concluded his introductory comments with a balanced and nuanced assessment of limits to Snow's originality and influence on the thinking of his contemporaries. He also lauded Benjamin Ward Richardson's memoir of Snow:

"It gives the picture of a man singu-[xx/xxi] larly endowed with the ability to think in straight lines and the courage to follow his own thought. In medicine these abilities placed him in the front ranks of his day; in epidemiology they carried him a generation beyond it." With such an endorsement, it will surprise no modern readers that the memoir Frost selected is the 1887 version, sanitized of embarrassing vestiges of mid-century medical thinking. Frost then upped the ante again, situating Snow amongst germ-theory epidemiologists. To do that, he needed to misrepresent Snow's cholera theory in modern vocabulary that Snow did not employ.

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