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).

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 [1] 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 [5], 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.”