A proposed chronology for the South London study
“latter part of” 1848, Snow develops new “opinions” and “views” about the pathology and mcc of cholera (MCC, 12; JPH-‘56, 239), apparently swayed in the following order:
** Snow’s researches on chloroform in 1848 may have caused him to rethink the pathology underlying his former view that cholera could be communicated as an effluvial infection producing fever:
“At a time when the chemistry of gaseous substances did not exist, and when certain diseases were attributed to a putrefaction of the fluids of the living body, these diseases were supposed to be occasioned by the effluvia given off during ordinary putrefaction. (“On the Chief Cause of the Recent Sickness and Mortality in the Crimea,” MTG (12 May 1855).
– pathology, as a local irritation of the mucous membrane of alimentary canal, not a “general illness . . . [that is] poisoning of the blood” (JPH-‘56, 239; also MCC, 8; PMCC, 745).
– “conclusive evidence” of person to person communication [cholera progress], which could be explained pathologically as local irritation and multiplication in alimentary canal, excreted, and passed on to others “when suitable opportunities occur” (JPH-‘56, 239).
– from personal observation, supplemented by published accounts [MCC, 10), he knew of two such opportunities: in the “crowded inhabitants of the poor,” where lack of color and odor of cholera evacuations made it more likely that residents would inadvertently ingest the poison (whereas a “social visitor” would not; and mining districts, where lack of sanitary conditions, extended work shifts, and absence of daylight could lead to the same outcome (JPH-‘56, 239). [n.b., the mining example does not occur in MCC, but does in PMCC].
– if cholera excretions could produce disease via ingestion, person-to-person, then the only way to scientifically (in sense of finding indisputable positive and negative evidence) explain the epidemic character of cholera is to assume cholera excreta diffused in drinking water could as well (JPH-‘56, 239-40; MCC, 11, on emptying of sewers into drinking water).
Winter 1848/49: mentions views to “several medical gentlemen,” including Garrod and Parkes MCC, 12). Then “sought anxiously, and waited patiently, for some confirmation” (JPH-‘56, 240).
– sends out letters of inquiry to various parts of the country and looks for published reports of incidents where cholera outbreaks where victims “had received, amongst other impurities, what must have come from a patient previously ill of the disease” (JPH-‘56, 240).
– earliest certain reply is from February 1849, about a well in Newburn, contaminated by run-off from a coal mine during 1831 epidemic [JS already knew of mortality figures, and then contacted Dr. Embleton, a friend from his apprenticeship days] (PMCC, 923).
– by August 1849, has information on towns where sewers empty into tidal rivers (Nith, Clyde, and Thames) from which drinking water is drawn, which had unusually high cholera mortality in 1831-32 and/or 1848-49 (MCC, 11).
– by end of August 1849, has established association in both 1832 and 1848-49 epidemics between high cholera mortality in south and east districts/regions of London and water supply taken from those parts of Rivers Thames and Lea with high sewer contamination (MCC, 11-12; (JPH-‘56, 240).
– Grant’s reports [?? July and early August?] on Horsleydown and Albion Terrace outbreaks –> Snow conducts own investigations and decides to complete MCC and personally publish it as a pamphlet [by my reading, the section on pathology was done much earlier; table on London mortality goes through 25 August, so that section was at least finished shortly before he sent it to the printer.]. Besides formulating own hypothesis, he decides to challenge Milroy’s effluvial explanation--ubiquity of odors, but not of cholera. (MCC, and again in “Cholera at Albion Terrace” in September).
September - November 1849: “Before the end of 1849 I was able to show [in PMCC] that a very close connexion existed between the mortality from cholera and the nature of the water supply, not only in London [at level B, perhaps, but surely not level C], but throughout the country. This connexion was very evident in certain towns, as Exeter and Hull, where the supply of water had been changed between the epidemic of 1832 and that of 1849. Where a polluted supply was changed for an unpolluted one, the cholera was almost prevented; and where a scanty but unpolluted supply had been changed for one contaminated with the sewage of the town, the epidemic prevailed to a fearful extent. [N.B. these two examples become Snow’s highest-probability evidence until he becomes aware of the change in water supply in intermixed SoLo districts at end of ‘53.] The attention of Dr. Wm. Budd and Dr. Farr was directed to this subject, with the result of confirming what I had stated” (JPH-‘56, 240).
[my hunch is that he took much of his information from the Health of Towns Reports, given my recollection of the towns it covers cf. PMCC, and that most of Snow’s inquiries from the winter of 48/49 initially came therefrom; but this is Nigel’s bailiwick]
– in PMCC on south London, notes change in supply for one borough between 1832 and 1848-49, but unable to draw a conclusion: “The part of the metropolis most severely visited by cholera in 1832, was the Borough of Southwark, in which 97 persons in each 10,000 of the population were carried off, being nearly three times the proportion of deaths that occurred in the rest of London. Now the population of Southwark at that time (such of them as did not use pump-water), were supplied by the Southwark Water Works with Thames water obtained at London Bridge, and sent direct to their dwellings without the intervention of any reservoir. The Thames has since become more polluted by the gradual abolition of numbers of cesspools in the metropolis, and the Southwark Water Works have been removed to Battersea, a little further from the sewers. I am endeavouring to compile a full account of the recent epidemic in London, in its relation to the water, but as it is not yet complete” (PMCC, 747).
1850 – nada
May-June 1851: delivers paper on MPC at Epi Soc, published (after some revisions, apparently) by MTG in October/November. At the Epi Soc he compares map from 2nd HoTR on distribution of water supply in London by different companies and Grainger’s colored map of differences in cholera mortality in the metropolis. Conclusion: “In London the cholera was most prevalent during both epidemics in those districts supplied with water vitiated by the contents of sewers and cesspools, and indeed it generally bore an exact relation to the amount of vitiation” (MTG 3: 610).
That is, he is still looking for at the district level for comparisons between “quality of drinking water” and cholera mortality–particularly between epidemics if the supply changes; cites Weekly Return for 12 January 1850 as substantiation (611).
– most of paper is recitation of pathological reasoning and examples from MCC and PMCC, as well as information received since 1849 on person-to-person transmission (contaminated cow-heels, etc.), polluted wells and ditches; emphasizes negative evidence bearing on the Milroy objection– public institutions with own wells and little cholera mortality, but situated in districts with high mortality.
January 1852: Lambeth Company moves source of supply from Lambeth works to Thames Ditton, “about a mile and a half above Kingston, and three miles beyond the influence of the tide” (Weekly Return, 19 November 1853, supplement).
1852: 15 & 16 Vict. cap 84 – “After 31st August 1855, it shall not be lawful for any company to supply London with water from any part of the Thames below Teddington Lock, or from any part of its tributary streams below the highest tidal point. An extension of . . . one year is granted to the Chelsea Company” (Ibid.).
May 1853: Paper on “Comparative Mortality of Towns and Rural Places” at Epi Soc. For present purposes, note that this contains dismissal of sanitary reform as explanation for lower mortality of young men in “worst”districts of London cf. to rural areas.
October 1853: “Prevention of Cholera” in MTG. Newcastle and Gateshead in 1853 epidemic support his theory. Water company changed supply to clean springs outside city. But increased demand for water during epidemic [to flush sewers?] caused company to also draw water from the Tyne –> geometrical increase in mortality in all classes using water, regardless of elevation; when people objected to impurity of water, company stopped drawing from the tidal part of the Tyne, only used spring water, and mortality dropped gradually due to normal propagation [no direct challenge to Milroy objection; JS has dismissed effluvia earlier in the pathology discussion of the paper]. (368).
Early November 1853: reiterates argument in letter to Times that cholera mortality in Newcastle proportional to impurity of water drawn from tidal river.
19 November 1853: Farr’s supplement on “Cholera and the London Water Supply,” Weekly Return. R-G’s Report on 1848-49 epidemic showed “that elevation of soil was the most constant and striking in its results; and that the influence of water supply, density of population, and wealth could also be detected in the progress of the epidemic. But it is evident that to estimate exactly the value of any of these forces, it is necessary to obtain similar conditions as regards the rest . . . . But of such experimenta crucis the circumstances of London do not admit.” Listing of water companies and their sources of supply – and, perhaps, where Snow first found out that Lambeth had shifted its source above the tidal reach of the Thames.
Then comes Farr’s conclusion: “From the above reports it appears that cholera finds London, as regards water, in the situation in which it left it. This holds true with reference to all except the Lambeth Waterworks Company, who changed their supply nearly two years ago . . . ; and from a Table subjoined it will be seen that the results of the present epidemic in the districts supplied by that company, as compared with others, are rather more satisfactory than they were in 1849 . . . .” [the comparison with ‘49 is not included in the table]. Then comes the table covering deaths through 12 November [n.b. not the table JS commented on in MCC2, 69], in which ratio of deaths per 100K in districts supplied by both S&V and Lambeth companies compared to S&V only-supplied districts is 56:85. Where Southwark overlaps with Kent, mortality was 101/100K. Beneath the table, Farr adds: “It is believed that through nearly the whole of this Table the impurity of the waters with which the inhabitants of the several districts are supplied is in nearly a direct proportion to the mortality from cholera.”
That is, Farr was the first to suggest that improved Lambeth supply reduced cholera mortality in parts of SoLo.
Snow never mentions this table, to my knowledge.
26 November 1853: Farr’s table in Weekly Return covering deaths through 19 November reaffirms the SoLo comparison of Lambeth and S&V, this time in ratio of 61 (intermixed) to 94/100K (S&V only). (JPH-‘56, 240; Lancet ‘55, 11). In Southwark and Kent intermixed, mortality had risen to 107/100K. Beneath the table: “*In three cases (marked with an asterisk) the same districts are supplied by two companies.” The asterisks do not appear in the table from the prior week’s return.
Snow reprints part of this table as table 4 in MCC2, 69, minus the asterisks.
Snow writes later: “In the autumn of 1853 it was shown by Dr. Farr* that the districts partly supplied by this, the Lambeth Water Company, with improved water, suffered less than the districts supplied entirely by the Southwark and Vauxhall Company with the water from the river at Battersea Fields, although in 1849 they had suffered rather [240/241] more than the latter districts” (JPH-‘56, 240-41). [*note is to Weekly Returns of Deaths, November.] [I cannot find where Farr compares intermixed with S&V only]
3 December 1853 Weekly Return: Deaths through 26 November, ratio of 64 (intermixed) to 102/100K (S&V only). (JPH-‘56, 240; Lancet ‘55, 11). In Southwark and Kent intermixed, mortality remained at 107/100K. Under the table, Farr wrote:
“It is a well known fact that the sewers, which receive the overflowings of the waterclosets, cesspools, and other sinks of impurity in London, flow at present into the River Thames and the River Lee, where, after dilution in the tidal waters, they are in various proportions variously mixed, and in some cases filtered, taken up by the pipes of the water companies, and pumped into the houses of the inhabitants of the metropolis for domestic use.
It is also a fact, well established by the observation, that the cause of cholera in an epidemic acts more or less on the whole of the population, but that its fatality bears a certain relation to the impurity of the soil, the water, and the air.
The dirty water and dirty air sink towards the bottom of the London basin, from which they also incessantly send up dank vapours; and it has been shown, that when large numbers are taken, so as to render other circumstances nearly equal, the mortality decreases progressively in the dwellings at different elevations.
After correcting the above Table and the tables of cholera 1848-49, for the effects of elevation, it is found that a large residual mortality remains, which is fairly referable to the impurity of the water; for it is least where the water is known to be sweetest, greatest where the water is known to be the most impure.”
[Is Farr leaning more toward Snow’s theory than he was in the Return a couple of weeks prior about the exp. crucis? Had Snow buttonholed him and suggested a re-evaluation of the 1848-49 figures?]
10 December 1853: Weekly Return supplement on “London Water Supply” included comments from registrar of Rotherhithe explaining the dramatic change in mortality in that district between 1848-49 (highest by far in London) to late December 1853 (about fifth) as due to increased public use of water in pipes supplied by Kent Water Company in the intervening years. Registrar states that 1848-49 figure “is quite in conformity with the general rule, that when cholera prevails, it is most fatal where the waters are most impure” (MCC2, 70). [N.B., that Snow often until commencing the SoLo Study referred to the same empirical “rule.”]
31 December 1853: Table (JS’s no. 5) from Weekly Return (covering deaths in first 17 weeks of epidemic from 21 August - 17 December by districts) shows that mortality in Lambeth at 34/100K, whereas at end of 1849 it was 120/100K (JS’s no. 3). “Rotherhithe also has been removed from the first to the fifth place; owing, no doubt, to the portion of the district supplied with water from the Kent Water Works, instead of the ditches, being altogether free from the disease, as was noticed above” (MCC2, 72).
Sometime between 26 November 1853 and January-February 1854: “I had learnt [note tense, with this passage coming after that in which he discusses his sub-district computations based on Farr’s table from January 1854] from the evidence of Mr. Quick in the Health of Towns Reports, that the division of the houses, between the Lambeth Company on the one hand, and the Southwark and Vauxhall Company on the other, was not such as obtains in the north districts of London, where a parish is often divided between two water companies, but where one company always leaves off at the point at which the other begins. Throughout the greater part of Lambeth and Southwark, the whole of Newington, and a part of Camberwell, however, the supply of the two companies above mentioned is actually intermixed, the pipes of both companies going down the same streets, in consequence of the active competition which once existed between three water companies, two of which have since amalgamated and come to an agreement with the other--the Lambeth company” (JPH-56, 241).
Extracts from testimony of Joseph Quick, Engineer at Southwark Water Company, before the Commission inquiring into the State of Large Towns and Populous Districts, 28 March 1844 (UK. House of Commons. Sessional Papers, 1844. Vol. 17; paper #572).
“5923. Do you filter the water supplied by the Southwark Water Company? — Yes, we have done so during the last three years and a half [since moving supply from London Bridge to Battersea].
5924. Do you attain the same degree of clearness that is attained by private filters? — I believe we do. . . . I consider when Thames water is purified by deposit and filtration, it is better than spring or Wandle river water, and softer and fitter for domestic purposes” (399).
. . . . . . . .
“5948. As the public are at present supplied in the Southwark district, how many capitals are invested, and how many sets of pipes traverse the same streets? — There are three companies, in some streets and three sets of pipes, in others two, and we have at the present the exclusive supply of about one-tenth of the district. On the average there may be said to be about two capitals in the same street. This is also the case with supplies of gas. In no part of the district is there less than two capitals in gas supplies in the same street, and in a very large portion three”(401).
With respect to when to date Snow’s re-acquaintance with Quick’s testimony (first ref to it is in PMCC) Snow says the following in MCC2: “London was without cholera from the latter part of 1849 to August 1853. During this interval an important change had taken place in the water supply of several of the south districts of London. The Lambeth Company removed their water works, in 1852, from opposite Hungerford Market to Thames Ditton; thus obtaining a supply of water quite free from the sewage of London. The districts supplied by the Lambeth Company are, however, also supplied, to a certain extent, by the Southwark and Vauxhall Company, the pipes of both companies going down every street, in the places where the supply is mixed, as was previously stated. In consequence of this intermixing of the water supply, the effect of the alteration made by the Lambeth Company on the progress of cholera was not so evident, to a cursory observer, as it would otherwise have been. It attracted the attention, however, of the Registrar-General, who published a table in the “Weekly Return of Births and Deaths” for 26th November 1853, of which the following is an abstract, containing as much as applies to the south districts of London” (68).
Problem is that he does not discuss the intermixing until several pages later: “The intermixing of the water supply of the Southwark and Vauxhall Company with that of the Lambeth Company, over an extensive part of London, admitted of the subject being sifted in such a way as to yield the most incontrovertible proof on one side or the other. In the sub-districts enumerated in the above table [ie., 6–the one he generated in Jan/Feb 1854] as being supplied by both Companies, the mixing of the supply is of the most intimate kind. The pipes of each Company go down all the streets, and into nearly all the courts and alleys. A few houses are supplied by one Company and a few by the other, according to the decision of the owner or occupier at that time [74/75] when the Water Companies were in active competition. In many cases a single house has a supply different from that on either side. Each Company supplies both rich and poor, both large houses and small; there is no difference either in the condition or occupation of the persons receiving the water of the different Companies.” [then follows the passage about the natural experiment]
** It would appear that Snow initially drafted the description of intermixing for an earlier part of MCC2, near the passage where he describes what Farr had presented in a table in November 1853. My construction is that once Snow saw the makings of a natural experiment in Farr’s return (table and description of London water supply), Snow recalled that Quick had said something about it when it mattered little since all three companies (in 1844) drew their water from polluted stretches of the Thames. First “Eureka” moment?
“To turn this grand experiment to account, all that was required was to learn the supply of water to each individual house where a fatal attack of cholera might occur. I regret that, in the short days at the latter part of last [75/76] year, I could not spare the time to make the inquiry; and, indeed, I was not fully aware, at that time, of the very intimate mixture of the supply of the two Water Companies, and the consequently important nature of the desired inquiry” (MCC2).
** Later, Snow’s recollections do not mention names: “My attention had been closely applied to the particulars of the water supply of London for upwards of five years before the epidemic of cholera of 1854; and I had, from various sources, became acquainted with a number of circumstances which made it possible for a very conclusive personal inquiry to be made, in respect to that kind of influence of water supply on cholera which I had published in 1849. These circumstances were necessarily known to a number of workmen and several official persons, but probably net in their collective form to any other person interested in the mode of propagation of cholera, except myself. The particular circumstances of the water supply, and its adaptation to the kind of personal inquiry which I conceived and undertook, were first published by me in the Medical Times and Gazette of September 2nd, 1854, p. 247, and were alluded to in a leading article in the Association Medical Journal for October 27th of the same year” (“Cholera, and the Water Supply in the South Districts of London,” BMJ 1 (17 October 1857): 864).
January-February 1854 [?? Nigel, could you check Vital Statistics to see if it gives a source for the following list, which I assume was in a supplement to a Weekly Return]: “As the Registrar-General published a list of all the deaths from cholera which occurred in London in 1853, from the commencement of the epidemic in August to its conclusion in January 1854, I have been able to add up the number which occurred in the various sub-districts on the south side of the Thames, to which the water supply of the Southwark and Vauxhall, and the Lambeth Companies, extends. I have presented them in the table opposite, arranged in three groups” (MCC2, 72; table 6). The three groups were the 12 sub-districts supplied by S&V only, 16 inter-mixed sub-districts, and 3 sub-districts supplied by Lambeth only.
In the discussion of table 6, Snow compares adjoining parishes of Christchurch (intermixed) and St. Saviour (S&V alone) [he does not have sub-district information for 1849]. Mortality in Christchurch parish in 1849 was “rather higher” than in St. Saviour [source of info is not stated; table 3 figures are by district], in 1853 mortality was 227/100K in St. Saviour sub-district cf. 43 in Christchurch sub-district. [Since he does not know the degree of intermixing, or precisely how many houses supplied by each company in Christchurch, he is forced to cite each company’s rated investment:] “The pipes and other property of the Lambeth Company, in the parish of Christchurch, are rated at about £316, whilst the property of the Southwark and Vauxhall Company in this [73/74] parish is only rated at about £108.” He also compares Waterloo Road, 1st part (intermixed) with St. Saviour in similar fashion (minus property rates), and two sub-districts in which Lambeth has few pipes cf. to S&V: “The sub-districts of Kent Road and Borough Road, which suffered severely from cholera, are supplied, through a great part of their extent, exclusively by the Southwark and Vauxhall Company; the supply of the Lambeth Company being intermingled with that of the other only in a part of these districts, as may be seen by consulting the accompanying map (No. 2)” (MCC2, 73-74).
[The manner in which the above is written–that is, unrevised for information about sub-districts he would accumulate in 1854–suggests to me that it was composed early in 1854, and relates to the following from JPH-56: “By showing the water supply in subdistricts, and thus getting a more correct line of demarcation, I was able to point out* that the advantage in favour of the population partly supplied with the purer water was even greater than Dr. Farr had indicated [in the Weekly Returns from November 1853]” (JPH-56, 241; *note is to MCC2, 73).
July - mid August1854: Epidemic returns in early July, but Snow decides to wait to begin house-to-house investigations until the Weekly Returns suggest that Farr’s observation in November 1853–“the results of the present epidemic in the districts supplied by that company [Lambeth], as compared with others, are rather more satisfactory than they were in 1849"–which Snow interpreted as “In the autumn of 1853 it was shown by Dr. Farr* that the districts partly supplied by this, the Lambeth Water Company, with improved water, suffered less than the districts supplied entirely by the Southwark and Vauxhall Company with the water from the river at Battersea Fields, although in 1849 they had suffered rather [240/241] more than the latter districts” (JPH-‘56, 240-41). Perhaps he’s referring to a personal communication.
“The mortality from cholera was much less during the epidemic of last autumn, in the districts to which the new supply of water extended, than in those districts which are exclusively supplied by the Southwark and Vauxhall Company. This will be seen on referring to a table in the return of deaths in London, for the week ending the 26th of November, 1853. Soon after the commencement of the present epidemic, the difference in the mortality of the respective sets of districts was equally apparent,—a difference which did not exist in 1849," “CC by Thames Water,” MTG 9 (2 September 1854).
“Observing, therefore when the cholera returned in 1854, that there was the same advantage in favor of the districts partly supplied with water from Thames Ditton, I determined to make an inquiry, the idea of which I had previously entertained . . . by ascertaining the water supply of every house in which a fatal attack of cholera might occur” (JPH-56, 241).
“When the cholera returned to London in July of the present year [recall it’s published in 1855], however, I resolved to spare no exertion which might be necessary to ascertain the exact effect of the water supply on the progress of the epidemic, in the places where all the circumstances were so happily adapted for the inquiry. I was desirous of making the investigation myself, in order that I might have the most satisfactory proof of the truth or fallacy of the doctrine which I had been advocating for five years” (MCC2, 76).
“I accordingly asked permission at the General Register Office to be supplied with the addresses of persons dying of cholera, in those districts where the supply of the two Companies is intermingled in the manner I have stated above. Some of these addresses were published in the “Weekly Returns,” and I was kindly permitted to take a copy of others” (MCC2, 76).
[Steve: you might be able to narrow the following windows of cholera-investigative opportunity by comparisons with his anesthesia schedule per the Casebooks.]
**Around 19 August 1854: Snow begins h-t-h investigations in two sub-districts containing an intermixed supply, using lists of deaths from cholera down to 12 August published in the Weekly Returns [any deaths listed in a weekly return to 12 August would have been in the following week, ie. 19 August].
“The particulars of all the deaths which were caused by cholera in the first four weeks of the late epidemic, were published by the Registrar - General in the ‘Weekly Returns of Births and Deaths in London,’ and I have had the three hundred and thirty-four above enumerated reprinted in an appendix to this edition” (MCC2, 80).
“For the first four weeks of the epidemic I employed the list of deaths from cholera published in the Weekly Returns Of the Registrar-General, and for the next three weeks, during which my inquiry extended, I was kindly permitted to copy the addresses of persons dying of cholera at the General Register Office” (JPH-56, 242).]
“I commenced my inquiry about the middle of August with two sub-districts of Lambeth, called Kennington, first part, and Kennington, second part” (MCC2, 76).
[Unclear to me why he chose these two sub-districts. They were in the middle of the pack in terms of ‘53 mortality. From his map in MCC2, it appears that Kennington 1st was part intermixed, part S&V only; and Kennington, 2nd was part intermixed, part Lambeth only. Statisticians on the team, please advise.]
* Seems reasonable that in this first part of the inquiry he would come to realize that the degree of intermixing of water supply was far greater than he had imagined, and made the experiment potentially more of a clincher for his theory than he could ever have imagined possible. If so, this is Snow’s second “Eureka” realization: “After commencing the inquiry I found that the circumstances were calculated for affording even more conclusive evidence than I had anticipated. The pipes of the two water companies not only passed down all the streets, but into nearly all the courts and alleys. A single house often had a different supply from that of either side. Each water company supplied alike both rich and poor, and thus there was a population of 300,000 persons, of various conditions and occupations, intimately mixed together, and divided into two groups by no other circumstance than the difference of water supply. One group supplied with water contaminated, to a large extent, [241/242] with the sewage of London, and the other receiving a supply altogether free from such impurity” (JPH-56).
Between 19 and 26 August 1854: Snow shows his data on the two sub-districts to Farr, who suggests that the inquiry be expanded to include all south London districts beginning on 27 August, to be carried out by his staff of registrars.
“There were forty-four deaths in these sub-districts down to 12th August, and I found that thirty-eight of the houses in which these deaths occurred were supplied with [76/77] water by the Southwark and Vauxhall Company, four houses were supplied by the Lambeth Company, and two had pump-wells on the premises and no supply from either of the companies” (MCC2).
“As soon as I had ascertained these particulars I communicated them to Dr. Farr, who was much struck with the result, and at his suggestion the Registrars of all the south districts of London were requested to make a return of the water supply of the house in which the attack took place, in all cases of death from cholera. This order was to take place, after the 26th August, and I resolved to carry my inquiry down to that date, so that the facts might be ascertained for the whole course of the epidemic” (MCC2, 77).
“I gave a copy of the first results of my inquiry to Dr. Farr, to whom I was indebted for facilities very kindly afforded: and Dr. Farr being much struck with these results, instituted a continuance of the inquiry through the district [242/243] registrars, who were requested to make a return of the supply of water to each house in which a fatal attack of cholera might occur ill all the south districts of London” (JPH-56).
But what did he mean by “my inquiry”? At this point, his experiment was limited to the intermixed areas, only: “I pursued my inquiry over the various other sub-districts of Lambeth, Southwark, and Newington, where the supply of the two Water Companies is intermixed, with a result very similar to that already given, as will be seen further on. In cases where persons had been removed to a workhouse or any other place, after the attack of cholera had commenced, I inquired the water supply of the house where the individuals were living when the attack took place” (MCC2, 77).
At this point, he had decided against h-t-h inquiries in districts exclusively supplied by Lambeth because of distance and lack of a control: “The only districts which are supplied exclusively with the water from Thames Ditton, are such distant places as Balham, Streatham, Dulwich, and Sydenham, whose freedom from the epidemic might be attributed to other causes than the mere absence of the polluted water” [Milroy objection and/or Farr’s elevation and/or sanatorians] (“CC by Thames Water,” MTG 9 (2 September 1854)).
Between 27 August and end of month, 1854: Snow completes investigations in two more sub-districts, Waterloo parts 1 and 2, for deaths down to 19 August [which if he copied them from the Weekly Returns means that he could not have begun until the return ending 26 August was printed]. Second results confirm first results, although he found some houses containing more than one death so he adjusted the table prepared for MTG accordingly.
He knows the water companies have supplied Parliament and the BoH with information about the number of houses in the above districts (Lambeth, Newington, etc.), and assumes that he can generalize therefrom to sub-districts:
“According to the returns made by the water companies to Parliament and to the Board of Health, there are quite as many houses supplied by the Lambeth as by the Southwark and Vauxhall Company, in the above districts; and both Companies supply alike all kinds of houses, —those of the rich and the poor indiscriminately. It is evident, therefore, that, in the sub-districts to which the inquiry has extended, the people having the improved water supply enjoy as much immunity from cholera as if they were living at a higher level, on the north side of the Thames” (“CC by Thames Water,” MTG 9 (2 September 1854)).
“CC by Thames Water” functions for SoLo/MCC2 very much like MCC did for PMCC–the preliminary data are too suggestive to wait for the completed study after Farr’s registrars carry the investigation through to the end of the epidemic. “In the mean time, I have considered that the inquiry, even in its present stage, is too important to be withhold from the Profession, at a season when every week is adding so much to the mortality from cholera.”
By end of August Snow has established the distinction he needs for determining the supply source if the tenants are uncertain: “It [S&V water] also contains a much larger quantity of chlorides than Thames water obtained above the reach of the London sewage.”
He’s also established a visual test for possible sewage contamination. The water may appear clear to “careless observers,” but S&V water “contains organic matter, both in solution and suspension, and deposits a small quantity of whitish flocculent matter on standing.”
** First week of September 1854: Visits Lambeth and St. Saviour’s workhouses to investigate water supply and mortality (MCC2, 91).
3 September 1854 (Sunday): Snow hears about the outbreak in the Golden Square area and tests water of Broad Street pump.
“As soon as I became acquainted with the situation and extent of the late outbreak of cholera in Broad-street, Golden Square, and the adjoining street, I suspected some contamination of the water of the much frequented street-pump in Broad-street, near the end of Cambridge- street: but on examining the water, on the evening of the 3rd inst., I found so little impurity in it of an organic nature, that I hesitated to come to a conclusion” (“The Cholera near Golden Square,” MTG 9 (23 September 1854)).
4-5 September 1854: Continues testing water of Br. St. pump, finds that amount of organic impurities in it varies, and rules out other “circumstances” after “further inquiry.”
“Further inquiry, however, showed me that there was no other circumstance or thing common to the circumscribed locality in which this sudden increase of cholera occurred, and not extending beyond this locality, except the water of the above pump. I found, moreover, that the water varied, during the next two days, in the amount of organic impurity it contained; and I concluded that, at the commencement of the outbreak, it might have been still more impure” (MTG of 23 Sept).
“With respect to the pump wells, I found some impurities in the water of each of those which I examined in the first week of September, in the Golden Square district, except the one in Vigo Street. The water of the pumps in Broad Street, Warwick Street, and Bridle Lane, all contained impurities visible to the naked eye on close inspection, in the form of minute, whitish, flocculent particles” (CIC, 98).
5 September 1854: visits GRO, compiles list of 89 deaths through 2 September, establishes that epidemic began on Thursday 31 September, and thereafter begins h-t-h inquiries.
7 September 1854 (evening): has an “interview” with Governors and Directors of the Poor [not the Board of Guardians; St. James parish did not convert to a Poor Law Union until 1867, or so–it had received a special dispensation from implementing the New Poor Law]
“I had an interview with the Board of Guardians of St. James’s parish on the evening of Thursday, 7th September, and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day” (CIC, 102).
12 September 1854: Visits Deptford, and makes inquiries into cholera outbreak in two streets there. Makes additional inquiries into “all the surrounding streets” but finds no smoking gun.
*Between 16-23 September: Writes the letter for MTG about results of inquiries in Golden Square and Deptford. Knows from Weekly Return of 16 September about “the very large number of deaths that occurred in the week ending 9 September,” but decides against a full inquiry into them; thinks inquiry through 2 September is sufficient. But does make a few spot checks, as does Marshall on his behalf.
--states that his SoLo inquiry is almost finished: “I have very nearly concluded the inquiry respecting the comparative influence of the water of the Lambeth Water Company and that of the Southwark and Vauxhall Company, of which I gave some account in the Number of the Medical Times and Gazette of the 2nd inst. The result, which I shall communicate when completed, will show that among the population having the impure water of the Thames, from Battersea Fields, the mortality from cholera has been ten times as great as among the population having the improved water from Thames Ditton” (MTG of 23 Sept).
Second half of September:
First he completes investigations in the intermixed area: “The number of deaths from cholera down to August 26, in the sub-districts which are partly supplied by the Lambeth Water Company, was 642. Of these I found that the water supplied to the house in which the attack took place was, in 509 instances, that of the Southwark and Vauxhall Water Company; in 93 cases it was that of the Lambeth Company; and in the remaining 40 instances it was from other sources, or the supply was not ascertained” (“CC by Impure TW,”MTG of 7 October).
But when he seeks the denominator data he needs to determine the precise ratios of mortality in sub-districts/number houses supplied for each water co in those sub-districts, he is unable to find the desired information, although he thinks that it’s either already collected or will be soon: “I hope shortly to learn the number of houses in each sub-district supplied by each of the Water Companies respectively, when the effect of the impure water in propagating cholera will be shown in a very striking manner, and with great detail” (“CC by Impure TW,”MTG of 7 October).
– But there is data on total number houses supplied in all districts by each company, and he cites the following in early October: “The entire number of houses supplied by the Southwark and Vauxhall Company, according to a return made to the General Board of Health in 1850, was 34,217, and the number supplied by the Lambeth Company, according to the same return, was 23,396. The number of houses supplied by both Companies has increased with the extension of the Metropolis, but it is pretty certain that the proportion continues nearly the same, and for the sake of comparison, the number of houses may be supposed to remain the same also” (“CC by Impure TW,”MTG of 7 October).
-- Until he receives the desired information about water supply at the sub-district level, he decides to expand the inquiry beyond the intermixed sub-districts in order to at least make a regional comparison: “In the mean time, in order to be able to compare the mortality from cholera among the customers of each Company, with the entire number of houses supplied by each of them respectively, I thought it desirable to extend the inquiry to Rotherhithe, Bermondsey, Camberwell, and certain parts of Southwark, which are supplied by the Southwark and Vauxhall Company alone” (“CC by Impure TW,”MTG of 7 October).
– [my reading of this passage is that Snow considered the expansion a temporary expedient and less likely to prove his theory than the initial inquiry in the intermixed sub-districts “when the effect of the impure water in propagating cholera will be shown in a very striking manner.” If I’m correct, then Snow still considered the experimentum crucis to be a full analysis of the intermixed districts, only–which he would not be able to complete until he had denominator data for number of houses/sub-district/water co.]
– shortly after deciding on an expanded inquiry, Snow realized that he would be unable to complete it himself, given other responsibilities that began the first week of October [I assume he means administering anesthesia more frequently at hospitals in conjunction with the increase in surgeries during term when students could observe; Steve: would you confirm/falsify in CB?]. He decides to finish the three outlying sub-districts in which Lambeth Co is the only supplier (Norwood, Streatham, and Dulwich), and then engages and trains Whiting to survey the twelve S&V only sub-districts:
“I was unable by myself to execute this part of the inquiry before the commencement of the winter session, but I was fortunate enough to obtain the assistance of a medical man, Mr. John Joseph Whiting, L. A. C., who took great pains with this part of the inquiry. The inquiry thus extended reached over the whole of the districts on the south side of the Thames, except those of Greenwich and Lewisham” (“CC by Impure TW,”MTG of 7 October).
“I was fortunate enough to obtain the assistance of a medical man, Mr. John Joseph Whiting, L.A.C., to make inquiry in Bermondsey, Rotherhithe, Wandsworth, and certain other districts, which are supplied only by the Southwark and Vauxhall Company. Mr. Whiting took great pains with his part of the inquiry, which was to ascertain whether the houses in which the fatal attacks took place were supplied with the Company’s water, or from a pump-well, or some other source” (MCC2, 79).
– by late September or early October, Whiting had collected data for the first four weeks of the epidemic in the twelve S&V only subdistricts. For some reason, Whiting did not carry his h-t-h inquiries in those sub-districts down to 26 August:
“As regards most of the sub-districts, to which the water of the Lambeth Company does not extend, the personal inquiry reached only to the first four weeks of the epidemic, viz., to August 5 . . .” (“CC by Impure TW,”MTG of 7 October).
“Mr. Whiting’s part of the investigation extended over the first four weeks of the epidemic, from 8th July to 5th August; . . .” (MCC2, 79).
2 October 1854: Sends letter to MTG indicating that his personal inquiry into cholera mortality in all nineteen Lambeth-supplied sub-districts through 26 August is complete; letter published on 7 October.
“I have called at every house in which a death from cholera had occurred and been registered during the first seven weeks of the present epidemic, in all the sub-districts to which the supply of the Lambeth Water Company extends.”
– emphasizes that he recorded where attacks took place, not where deaths occurred: “In the cases of persons removed to a workhouse or any other place after the attack, I have extended the inquiry to the house in which the attack commenced.”
– describes in detail the test for chlorides he had devised by end of August: “This test is not liable to any fallacy.” These tests are done at home: “When the resident could not give clear and conclusive evidence about the Water Company, I obtained some of the water in a small phial, and wrote the address on the cover, when I could examine it after coming home.”
– In the table and discussion, Snow uses mortality figures from thirty-one sub-districts through 26 August, which includes a calculation for weeks five through seven [N.B. one asterisk indicating calculation appears by Clapham, which is in the intermixed area; there is none by Putney, which is S&V only] and calculates that mortality was nine times greater for S&V supply than for Lambeth.
* On basis of GBH figures from 1850 on total number of houses supplied by each company, and estimates of mortality in S&V only subdistricts for the three weeks that Whiting did not investigate, Snow concludes that mortality for the first seven weeks of the epidemic (through 26 August) was nine times greater in houses supplied by S&V.
– He also uses census data to show “the beneficial influence of the improved water on the progress of cholera,” but as with the table he is guesstimating.
** – Using census data and GBH figures, he suggests that the number of deaths in districts supplied by Lambeth is about the same or less than districts of higher elevation or otherwise “favoured”:
“But 93 deaths from cholera, the number which occurred in the population so supplied in these districts, is a proportion very little exceeding the mortality which had occurred at that time in the most elevated and favoured districts of the Metropolis, and much less than had happened in the West districts of London. It should he recollected, also, that a great portion of the population in the South districts are very poor, and are surrounded by all the conditions which have been generally supposed to favour cholera.” [including the Milroy objection]
– concerning the first four weeks of the epidemic, limits himself to a metropolitan comparison: “During the first four weeks of the present epidemic, 563 persons died of cholera in London. Of these it has been ascertained, by a personal inquiry at every one of the houses in which the attack took place, that no less than 268 of the fatal attacks took place in houses supplied with water by the Southwark and Vauxhall Company. A great part of the remaining deaths occurred in persons living or working among the shipping of the Thames, and who almost invariably draw their water direct from the river. During these four weeks there were but ten deaths from cholera in houses supplied with water by the Lambeth Water Company; although it has been shown above that they supply fully two-thirds as many houses as the other Company. The cholera was consequently eighteen times as fatal among the population supplied with the water from Battersea Fields as among that with the purer water from Thames Ditton, during these four weeks, although this latter population is intimately mixed with the former.”
– fires major broadside at the sanitarians: “The cholera of 1849 was much more fatal in London than that of 1832; the present epidemic has been more fatal in the districts supplied exclusively by the Southwark and Vauxhall Company than that of 1849; and if the Lambeth Company had not changed their source of supply the mortality in London would have much exceeded that of 1849. There is one circumstance, however, that ought to prevent any expression of blame or recrimination for the propagation of cholera in this way; it is this, –that the persons who have been most instrumental in causing the increase of cholera, are precisely those who have made the greatest efforts to check it, and who have been loudest in blaming what they considered the supineness of others. In 1832, there were few water-closets in London. The privies were chiefly emptied by nightmen, a race who have almost ceased to exist; or a portion of the contents of the cesspool flowed slowly, and after a time, into the sewers. By continued efforts to get rid of what were called the removable causes of disease, the excrement of the community has been washed every year more rapidly into the river from which two- thirds of the inhabitants, till lately, obtained their supply of water. While the fæces lay in the cesspools or sewers, giving off a small quantity of unpleasant gas having no power to propagate specific diseases, they were spoken of as dangerous and pestilential nuisances; but, when washed into the drinking- water of the community, they figured only in Sanitary Reports as so many grains of organic matter per gallon.
After MTG October piece and when preparing MCC2: he finds new info on total number of houses that indicates he was a bit off in his supposition in October that expansion of piped water by water companies since 1850 would be in same proportion. So reworks data on basis of a different report: “According to a return which was made to Parliament, the Southwark and Vauxhall Company supplied 40,046 houses from January 1st to December 31st, 1853, and the Lambeth Company supplied 26,107 houses during the same period” (MCC2, 80). [my guess is that the return was generated by GRO at end of 1853 and included in the table(s) that Farr published in January 1853 on cholera mortality/districts, and which Snow then reworked for sub-districts and later published as table 6 in MCC2.]
End of chronology distributed on 19 February.
– Slightly reworks significance and justification of the expanded inquiry as a corollary to the experimentum crucis (intermixed districts).
“A return had been made to Parliament of the entire number of houses supplied with water by each of the Water Companies, but as the number of houses which they supplied in particular districts was not stated, I found that it would be necessary to carry my inquiry into [78/79] all the districts to which the supply of either Company extends, in order to show the full bearing of the facts brought out in those districts where the supply is intermingled” (MCC2, 78-79).
That is, the expansion is no longer a temporary measure until he receives more detailed data on water supply for each company; it has become part of a larger study of all sub-districts supplied by the two water companies.
– in light of the new information on numbers of houses supplied by each company, he revises the proportional mortality during the first four weeks of the epidemic:
“The cholera was therefore fourteen times [not eighteen, as in MTG] as fatal at this period, amongst persons having the impure water of the Southwark and Vauxhall Company, as amongst those having the purer water from Thames Ditton” (MCC2, 80).
– Devises table 7 that shows mortality by sub-districts in first four weeks of the epidemic (through 5 August) (MCC2, 84). Sydenham added to sub-districts served by Lambeth only – now four of those.
– Revises table from MTG 7 October (and includes it as table 8 in MCC2) “on account of the Water supply having since been ascertained in some cases in which I did not then know it. The small number of instances in which the water supply remains unascertained are chiefly those of persons taken into a workhouse without their address being known” (MCC2, 83).
– Then calculates proportion of deaths/10K during first seven weeks of epidemic (table 9): “The mortality in the houses supplied by the Southwark and Vauxhall Company was therefore between eight and nine times as great as in the houses supplied by the Lambeth Company; and it will be remarked that the customers of the Lambeth Company continued to enjoy an immunity from cholera greater than the rest of London which is not mixed up as they are with the houses supplied by the Southwark and Vauxhall Company” (MCC2, 86). [the intermixed sub-districts remain his prime concern]
14 October 1854: Weekly Return contains Farr’s estimate of population of houses supplied by S&V and Lambeth water companies (MCC2, 88) [that is, Farr does not have sub-district numbers at this point].
After 21 October 1854: Snow incorporates Farr’s registrar-collected data on water supply where cholera mortality occurred during second half of epidemic (weeks eight through fourteen), and reprints Farr’s table (as table 10 in MCC2). Then takes 795 cases where water supply was “not ascertained,” distributes them proportionally (“equally”) among the companies and comes up with new figures for S&V and Lambeth, adds the deaths to those from first seven weeks and revises table 10 accordingly, and attaches Farr’s population estimate from 14 October for a new table (table 11). Conclusion:
“We see by the above table that the houses supplied with the water from Thames Ditton, by the Lambeth [88/89] Company, continued throughout the epidemic to enjoy an immunity from cholera, not only greater than London at large, but greater than every group of districts, except the north and central groups.”
After 28 October 1854: Uses Farr’s table published in Weekly Return of 28 October, listing mortality by sub-districts through 21 October, in tripartite format set up in tables 6, 7, 8 to compare 1854 mortality to date with 1849 epidemic (the latter drawing on Farr’s Report on Cholera) in table 12.
“The table exhibits an increase of mortality in 1854 as compared with 1849, in the sub-districts supplied by the Southwark and Vauxhall Company only, whilst there is a considerable diminution of mortality in the sub-districts partly supplied by the Lambeth Company” (MCC2, 89).
Snow said that the extent of his inquiries in the workhouses of South London supported his general conclusion where he could determine both the water supply and the mortality. In 1849, his investigations for PMCC had focused on workhouses not supplied by the water companies, so he has no basis for comparison on relative mortality by companies: “I trust, however, that the Registrar [91/92] General, in giving an account of the recent epidemic, will make a return of the deaths amongst the inmates of the various workhouses and other institutions on the south side of the Thames, together with the water supply of the buildings. Bethlehem Hospital, the Queen’s Prison, Horsemonger Lane Gaol, and some other institutions, having deep wells on the premises, scarcely suffered at all from cholera in 1849, and there was no death in any of them during the part of the recent epidemic to which my inquiry extended” (MCC2).
South London analysis ends for MCC2 on p. 92, although there are several references thereafter to specific information garnered as well as the conclusions already noted. Therefore, the SoLo portion of MCC2 covers 24 pages of 137 pages of text.
Late November 1854: goes to Battersea–perhaps for the first time–and tests salinity of Thames water drawn directly from the river:
“I thought at first that the quantity of common salt, previously [95/96] mentioned as being present in the water of the Southwark and Vauxhall Company, consisted entirely of the salt which had passed down the sewers into the river, for I had no idea that any admixture of sea water reached as high as Battersea Fields. Mr. Quick, the engineer of the above Company, informed me, however, that an impregnation of salt water does extend as far after a long course of dry weather. It is obvious that a dry season whilst it increases the quality of impurity in the Thames, must also cause the sea water to flow further inland than at other times. I did not examine the water of the Thames in August or September, but I have done so now, at the latter part of November, and I am inclined to think that even yet a slight admixture of sea water may reach to Battersea Fields with every tide. I found 5.8 grains of chloride of sodium per gallon in water obtained at Hungerford Market, at half-flow of the tide, on 19th November, and 19.1 grains per gallon, in water obtained at the same place, on 27th November, at an hour and a half before high water; whilst water obtained at the London Bridge, on 28th November, at high water, contained 63.3 grains per gallon” (MCC2, 96).
However, Snow does not revise/update the SoLo section of MCC2, written in late October/early November, to reflect mortality in last two weeks of epidemic (22 October - 4 November). He does that later:
“During the last ten weeks of the epidemic, from August 27th to November 4th inclusive, 3,564 deaths occurred in the districts to which the supply of the two water companies extends, and the returns of the district registrars showed that in 2,443 cases the water supply of the house in which the fatal attack took place was that of the Southwark and Vauxhall Company; in 313 cases it was that of the Lambeth Company; in 207 instances the supply was from pump wells and other sources independent of the two water companies, and in 601 instances the supply was not ascertained.* These numbers show a mortality of 916 to each 100,000 inhabitants supplied by the Southwark and Vauxhall Company, [244/245] and 180 to each 100,000 supplied by the Lambeth Company; consequently at this period of the epidemic, the mortality was still more than five times as great amongst the population supplied by the former company as amongst that supplied by the latter” (JPH-56; the reference is to Weekly Returns for 1854, pp. 514-18).
11 December 1854: Writes preface to MCC2. My reading of the following entry is that Snow considered the south London inquiry incomplete at the point he finished writing MCC2:
“The results of my inquiry into the supply of water were, of course, obtained separately for each district and subdistrict in which the inquiry was made, and were so published; but I was unable at the time to show the relation between the supply of houses in which fatal attacks took place, and the entire supply of each district and subdistrict, on account of the latter circumstance not being known. I expressed myself as follows in an article which I published soon after my inquiry was made: “I hope shortly to learn the number of houses in each subdistrict supplied by each of the water companies respectively, when the effect of the impure water in, propagating cholera will be shown in a very striking manner, and with great detail.”* (JPH-56, 245; reference is to MTG for 7 October 1854).
12 December 1854: completes “Report on the water” for CIC.
From the concluding page: “I have been making inquiries during the autumn just passed, in the South districts of London, which shew that the dejections of Cholera can reproduce the disease after passing down the sewers into the Thames, and being afterwards distributed through some miles of the pipes of a water company. Under these circumstances, the cases of Cholera are scattered over the whole of the districts supplied by the company; and become gradually more numerous, as each set of cases, the dejections of which pass into the river, produces new ones. In the instances, on the other hand, in which a pump well, or some other local supply of water is thus contaminated, the outbreak is always sudden and violent” (“Dr. Snow’s Report,” CIC, 120).
Latter part of 1854: “At the latter part of 1854, the General Board of Health procured from the two water companies, by order of the Secretary of State, a list of all the houses which they supplied, which lists are very valuable, as affording the means of ascertaining the exact water supply of each district and subdistrict separately. By direction of the Scientific Committee of the Board of Health, the lists have been employed in making a supplemental inquiry into the effect of the water supply on cholera. For this purpose they were compared with the lists of deaths at the General Registrar Office, and the results” were included in Simon’s Report to the Board of Health in summer/fall of 1856 (JPH-56, 248).
Early January 1855: Advertisements in medical journals indicate that MCC2 is available at Churchill’s.
Wednesday 28 February 1855: At RoMed&ChirSoc, Edward Smith, M.D., reads a paper “On the Primary or Essential Seat of Cholera.” The Lancet reporter noted: “The aim of the author, in this communication, was to establish the doctrine that the essential seat of cholera was the organic or sympathetic system of nerves. A very elaborate argument [follows]. . . .”
“The paper was accompanied by an Appendix, with some Diagrams, exhibiting the relation of the epidemic cholera of 1849 and 1854, with the general mortality, and with the various questions in respect of temperature.”
Snow was the first to comment: “he considered nothing was more satisfactorily proved respecting cholera than that it was communicated from person to person. But the communication of a disease required a morbid material passing from one individual to another. A malady could not be propagated by any immaterial influence. Dr. Smith was, however, possibly one of those who disbelieved the communicability of cholera, and therefore he would state some other objections there were to Dr. Smith's views.” After reviewing his theory of cholera pathology and person-to-person communication, he stated: “An important manner in which that disease was propagated was through the drinking water. He had been able to prove this very clearly, as he considered, last autumn. The greater part of Lambeth and Southwark, and the whole of Newington, were supplied by two water companies, whose pipes were intimately mixed, each company supplying all classes of the community. One of those companies, about two years ago, began to supply water from Thames Ditton, quite free from the sewage of London, whilst the other company continued to supply it from the Thames a little above Vauxhall-bridge. Having been favoured by the Registrar-General with the addresses of persons who died of cholera throughout these districts, he (Dr. Snow) went to the respective houses, and he found that, in the first four weeks of the late epidemic, the mortality was fourteen times as great in the houses supplied by the last named water as in those supplied by the purer water from Thames Ditton. As the epidemic advanced, the disproportion became not quite so great, owing to the mixing of the people, but it remained very striking–about seven to one.”
Thursday 1 March 1855: Annual meeting of RoMed&ChirSoc, with election of officers for the 1855-56 session: John Simon, F.R.S., elected a member of the Council, but not an officer. Snow not elected to Council.
April 1855: Writes “On the Chief Cause of the Recent Sickness and Mortality in the Crimea”; published in MTG on 12 May.
– Re-iterates that his SoLo inquiry was an experimentum crucis: “The communications which I made to the Medical Times and Gazette in September and October last, respecting the influence of the water-supply on the prevalence of cholera in the south districts of London, showed very clearly that this disease may be propagated by water containing the evacuations of cholera patients. The conditions were remarkably favourable for the inquiry I undertook; the circumstances and situation of a very large population were exactly the same in every particular, except that a part received a water supply containing the sewage of London, and another part intimately mixed with it, had a water-supply quite free from such contaminations Whilst the former part of the population suffered excessively from cholera, the latter suffered no more than the population of London on the north of the Thames. The inquiries of the Registrar-General, taken up at the point at which I left off, and continued to the end of the epidemic, entirely confirmed these results.
– distinguishes level C from levels A&B communication: “if the excess of cases was merely occasioned by the ordinary impurity of the water always present, it would be distributed over the whole time of the epidemic, instead of occurring in one sudden and intense outbreak.”
– Uses SoLo study of contaminated drinking water as confirmation for person-to-person communication (an example of reverse inductive method): “The proof of the communication of cholera through the medium of water, of course completely confirms the fact of its propagation in a more direct way, by swallowing the morbid poison without the water, the crowded dwellings of the poor, in coal pits, and other situations.”
– suggests that a chemical understanding of gases rules out effluvia as a scientific explanation for the communication of infectious diseases: “At a time when the chemistry of gaseous substance did not exist, and when certain diseases were attributed to a putrefaction of the fluids of the living body, these diseases were supposed to be occasioned by the effluvia given off during ordinary putrefaction. These opinions have still a certain number of adherents, even in official quarters, [a left jab to the reasoning of Simon?] and it is worthy of the attention of those individuals that the greatest mortality in the Crimea took place at a time when the temperature was too low for putrefaction to go on, and when it was especially noticed that though many dead horses were lying about they emitted no smell.”
May and June 1855: Snow reads a paper, “On the communication of Cholera Through the Medium of Water,” at the Epidemiological Society. Lancet gives a reporter’s summation, only, (but a revised version appeared in MTG in July):
– Snow began by referring to 1851 paper he read before the society which detailed “the circumstances connected with the pathology of cholera, and with its history as an epidemic, which led him to the conclusion that the disease is propagated by the morbid poison which produces it being accidentally swallowed [sic]”
– confines remarks “chiefly to a single example [“of the communication of cholera through the medium of water”] on a large scale, which took place in the south district of London . . . .” Then follows repeat of what he had written elsewhere, often verbatim, about the SoLo study.
– affirms that his initial intention was only to study the “intermingled” supply, but only had an estimate that the Lambeth Company supplied “considerably more than half the houses in the sub-districts in which the water supply is mixed . . . .”
– “In order to get an exact result, by comparing the deaths amongst the customers of each water company, with the entire number of houses supplied by each company, as indicated in their returns to Parliament,” Snow obtained Whiting’s help “and extended his inquiries to all the districts and sub-districts to which the supply of either company extended.”
– argues that the water in the SoLo studied “conveyed the specific cause of cholera, and did not act as a mere predisposing cause.”
– dismissed the Milroy objection.
– J. G. French was first commentator: Snow and Whitehead have converted him to their views, based on their labors in SoLo and Golden Square.
– Dr. Rogers dissents, and is upset that a case of one of his patients has been used to support Snow’s views; it was “simple diarrhœa.”
14 and 28 July 1855: “Publication of Further Remarks on the Mode of Communication of Cholera; including some comments on the recent Reports on Cholera by the General Board of Health” in MTG.
– The natural experiment described: “The whole of the south districts of London, with the exception of the Greenwich district, and part of the Lewisham and Rotherhithe districts, are supplied with water by two water companies, one called the Lambeth Company, and the other the Southwark and Vauxhall Company. The population of the districts supplied by these two water companies, amounted in 1851 to nearly half-a-million. Now throughout the greater part of the districts supplied by these two water companies, the supply is intimately mixed, the pipes of both companies going down all the streets, and into almost all the courts and alleys. The water companies were at one time in active competition, and any person paying the rates, whether landlord or tenant, could change his water company as easily as his butcher or baker, and although this state of things has long since ceased, and the companies have come to such an arrangement that the people cannot change their supply, yet the result of the former competition remains. There is here and there a row of houses having the same supply, but very often two contiguous houses are supplied differently. There is no difference in the circumstances of the people supplied by the two companies; each company supplies both rich and poor alike” (32).
– natural experiment only became possible after the 1849 epidemic: “In 1849 the water supplied by the two companies was nearly the same;” but “between the epidemic of 1849, and that of 1853, a very important change was made in the water supply of a great portion of the south districts of London. The Lambeth Company removed their works in 1852 from the neighbourhood of Hungerford Bridge to Thames Ditton, which is situated above Teddington Lock, and is, therefore, beyond the influence of the tide, and out of reach of the sewage of London” (32).
– Farr turned his attention to water supply after MCC in 1849, then again in late 1853, “showing that the districts, partly supplied with the improved water from Thames Ditton, suffered a lower mortality than these supplied exclusively with the water from Battersea-fields. It was desirable, however, to investigate this matter more in detail, and to find out, if possible, what was the actual water-supply in the houses in which fatal attacks occurred. I was unable to do this in the epidemic in the last quarter of 1853, but when the cholera returned to London in the following summer, I resolved to call myself at the houses in which deaths might occur, in the districts where the water-supply is intermingled in the way I have explained” (32).
– decided to extend inquiry when he lacked denominator data for the intermingled area: “The number of deaths I inquired after personally amounted to 658; but as the water companies make no return of the number of houses they supply in particular parishes or districts, it was necessary, in order to find out the exact influence of the water, to extend the inquiry to all the districts to which the water of either company is distributed, in order that the number of fatal attacks might be compared with the entire number of houses supplied by each company” (32).
– crucial experiment still unfinished: “It is to be regretted that we have not yet the exact number of houses supplied by each water company respectively, in those sub-districts in which the supply is intimately mixed up, as it is there that the investigation approaches completely to a crucial experiment. Dr. Farr has all the data for ascertaining this point, and I hope it will soon be worked out. In the mean time, however, we can arrive very nearly at the truth by the help of the Census tables” (33).
– but we do have “perfectly correct” results “when the whole of the districts supplied by each of the companies are taken together, and compared with the entire number of houses supplied by each” (33).
– rejects Farr’s elevation theory: “the remarkable relation of an inverse nature, which Dr. Farr discovered to exist between the elevation of the soil, and the mortality of cholera in the metropolis, depended entirely on the relative purity or impurity of the water; taking into account not only the supply of the companies, but also that drawn from the Thames and tidal ditches, and that of the pump-wells, which are most liable, to pollution in the low-lying districts” (34).
– dismisses sanitarian theory of impure water as a predisposing cause and both local miasmatic (impure air) and contagious (infection) notions of effluvia as a cause of cholera.
July 1855: S&V moves its supply to Hampton.
26 June 1856: Letter to the Times, reacting to “a leading article” in previous day’s issue on Simon’s report to the Board of Health:
“This report, although valuable in some respects, contains, from the nature of it, only an approximation to the truth. The population supplied with the impure water of the Southwark and Vauxhall company suffered a mortality from cholera in the late epidemic not merely three and a half times as great as that supplied by the Lambeth Company, but six times as great; and even this fact expresses the influence of the impure water in an inadequate manner, unless the different periods of the epidemic are considered separately. The inquiry which supplies the matter for Mr. Simon’s report was not an original one undertaken during the epidemic, but an additional investigation made under very disadvantageous circumstances after the epidemic was over.
– then lays out the results of his own inquiry, by three periods: “In the first four weeks of the epidemic the deaths from cholera were 14 times as numerous among the population supplied with the impure water of the Southwark and Vauxhall company as among that supplied with the better water of the Lambeth Company, taking into account the respective number of these populations. In the next three weeks the mortality was 7 ½ times as great, and in the last ten weeks of the epidemic nearly five times as great in one population as the other, or, taking the whole epidemic, the difference was as 6 to 1.”
– Simon’s report is further flawed if one seeks to compare cholera mortality with water supply: “The inquiry conducted by Dr. Farr, of the General Registrar-office, and myself referred to the houses in which the fatal attacks took place; that of Mr. Simon refers to the houses in which the deaths occurred.”
– now that the natural experiment is no longer possible, Snow again points to connections between general mortality and impure water: “many other diseases, beside cholera, can be shown to be aggravated by water containing sewage, and that since the Southwark Water Company has obtained a supply almost equal in purity to that of the Lambeth Company the mortality of the south districts of London had greatly diminished.”
Summer? of 1856: “Cholera and the Water Supply in the South Districts of London, in 1854" published in JPH&SR 2 .
– first four pages recapitulate MCC –> MCC2.
– the denominator problem that prevents him from concluding the crucial experiment: “The results of my inquiry into the supply of water were, of course, obtained separately for each district and subdistrict in which the inquiry was made, and were so published; but I was unable at the time to show the relation between the supply of houses in which fatal attacks took place, and the entire supply of each district and subdistrict, on account of the latter circumstance not being known” (245). Then he cites his hope in October 1854 to have this information in short order.
– “This information did not, however, come within my reach till recently, and not even then with all the accuracy I could desire” (245). Then he highlights problematical aspects “in the Report on the Cholera Epidemics of London as affected by the Consumption of Impure Water, lately written by Mr. Simon, and published by the General Board of Health” (245).
– “there is a statement of the number of houses supplied by each of the water companies respectively in each district and subdistrict. The line has not been very accurately drawn where a street, as often happens, is partly in one district and partly in another; and thus, in the recent Report, the subdistricts of St. Saviour's, Southwark, Leather market, Bermondsey, Battersea, and Peckham, have been represented to contain a few houses supplied by the Lambeth Company although they do not contain any” (245).
– “There is also a further imperfection in the account of the water supply of the subdistricts. The numbers which are stated to represent the houses supplied by each water company in each subdistrict are found on adding up the tables not to do so, but to represent the number of houses, minus those situated in streets in which no death occurred; the latter being [245/246] placed all together at the end of each group of subdistricts which constitutes a district. Streets vary in size from one or two houses to two or three hundred, and the small streets would obviously be the most likely to be exempt from mortality; it could, therefore, do little good to distinguish such streets;”
– “The number of houses in these exempted streets is about one-ninth of the whole. Instead of being able to compare, as I could wish, the mortality in the houses supplied by each company with the exact number of houses supplied, I have only been able to compare it with the number of houses in the streets in which deaths occurred. This will necessarily raise the proportion of deaths about one-ninth; but there is every reason to believe that the relative proportion of deaths in the population supplied by the two companies respectively, which is the real object of the inquiry, will remain almost unaltered” (246).
Then Snow attempts to tie off the crucial experiment, best he can with the denominator data from Simon’s report and the fact that the data from Farr’s registrars was published in the Weekly Returns by districts: “As the first four weeks of the epidemic did not furnish a sufficient number of cases in all the subdistricts to serve for a statistical inquiry in detail, I have commenced by taking the first seven weeks of the epidemic collectively; and the first of the tables which accompanies this paper exhibits the results of my personal inquiry, when placed in connexion with the number of persons and houses supplied in each subdistrict by each water company respectively.* (246; the reference is to table 8 in MCC2, noting that the deaths listed are taken therefrom).
– conclusion: “The reader will observe from the last division of the table  that the proportion of deaths was, in every subdistrict, very much greater amongst the population supplied by the Southwark and Vauxhall Company than amongst that supplied by the Lambeth Company, and that the relative mortality is nearly the same throughout, except in two or three instances, where there were but one or two deaths for the basis of calculation amongst the customers of the Lambeth Company” (246).
– N.B. that a comparison of table 8 in MCC2 and table 1 in JPH shows that Lambeth-supplied sub-districts have altered: Clapham moved to S&V only, Wandsworth and Putney shifted from S&V only to intermixed. And I’m confused–how did Snow personally investigate the latter two if he thought in 1854 that they were S&V only?
– collapses the sub-district figures for first seven weeks from his and Whiting’s inquiries (in table 2–three weeks of which were computed, not h-t-h results) into “a more compact form, to show the result of the inquiry during the first part of the epidemic, arranged in districts” (247) to set up table 4.
– “The fourth table contains the results of that part of the inquiry made by Dr. Farr, when compared with the population supplied by each water company respectively. It is necessarily arranged in districts – for the results were so published in the Weekly Returns* – and not in subdistricts” (247; citation to Weekly Returns for 1854).
– table 5 compares actual mortality in all sub-districts supplied by the two water companies with calculated mortality and finds the two are very closely related: I have also calculated the number of deaths which would have taken place in each subdistrict according to the number of persons supplied with water by each company respectively, and in accordance with the mortality ascertained for the whole of the population supplied; and it will be observed that the calculated mortality bears a very close relation to the real mortality in each subdistrict” (248).
-- “This relation exists with regard both to the gross mortality and to the mortality to each 10,000 living, all through the table , and proves the overwhelming influence which the nature of the water supply exerted over the mortality, overbearing every other circumstance which could be expected to affect the progress of the epidemic” (248).
– Therefore, the tentative results published in 1854 are now proven: “Taking this inquiry altogether, and considering. that the results which were published two years ago, and could only be estimated collectively, are now corroborated in detail through upwards of thirty subdistricts, it probably supplies a greater amount of statistical evidence than was ever brought to hear on a medical subject” (248).
17 October 1857: “Cholera, and the Water Supply in the South Districts of London” published in BMJ. Snow reacts to a recent article that uncritically accepted the conclusions from Simon’s Report, including the 3.5 figure for relative mortality in the houses supplied by the two water companies.
– emphasized a major difference between his inquiries and those referred to in Simon’s report: “I called myself at every house from which a cholera death had been registered, in the first seven weeks of the epidemic of 1854, in all the districts in which the supply of the two Water Companies in question was intermixed ; and, if the illness had not commenced in the house in which the death took place, I then sought the real place of attack, and in either case I ascertained the water supply of the house. I did not rest satisfied with a mere verbal reply; but obtained, in all cases, such corroborative evidence as could leave no doubt on the point, and I have the notes of my result.”
– there was a parallel inquiry during the epidemic in one sub-district: “As a proof of their general correctness, I may mention that Mr. Greenwood, the very intelligent registrar of Christchurch, Southwark, made an inquiry on the same point for the same seven weeks, in his district, and, on our comparing notes, our results were exactly the same in every instance, although our respective inquiries had been conducted in a different manner.”
– considers the JPH article the conclusion of the study: “I have, moreover, shown in an article in the Journal of Public Health for October 1856, that the whole of the inquiry agrees with the relative mortality of the different districts and sub-districts supplied in varying proportions by the two Water Companies, both at different periods of the epidemic, and for the whole epidemic, in such a manner as could not happen unless the results of the inquiry were substantially correct.”
– explains why he thinks the Simon data is flawed: “The results of the above inquiry having been canvassed by the Scientific Committee of the General Board of Health, a further inquiry was instituted, and was carried out within the eighteen months following the epidemic, and furnished the numbers quoted in the Journal of the Association. This further or supplemental inquiry was conducted as follows. Lists of the houses supplied by each Water Company were obtained from the two companies, and these lists were compared with the lists of deaths from cholera at the General Register Office. There are several reasons, however, why an inquiry thus conducted could only supply an approximation to the truth, and could bear no comparison, in point of accuracy, with a personal inquiry made on the spot, at the time of the epidemic.”
– “It so happened that the lists supplied by the Lambeth Water Company (that with the purer water) are so arranged and explained that every place might be made out, unless when the above mentioned difficulty about numbers occurs; but the lists supplied by the Southwark and Vauxhall Company are made out in such a manner as to be of only very partial service. They have a kind of alphabetical arrangement . . . .”
– “we may conclude that the supplemental inquiry of the General Board of Health into the influence of water supply on cholera is of some value, and corroborates the original investigation, but ought by no means to be quoted as an exact exposition of facts, or be allowed to set aside the previous inquiry.”