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"Letter to the right honourable Sir Benjamin Hall, Bart., President of the General Board of Health"

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(12 July 1855)

Original pamphlet courtesy of the Historical Library, Yale University Medical School

By John Snow, M.D.

Member of the Royal College of Physicians, and President of the Medical Society of London.

I was ordered, as you are aware, to give evidence before the Select Committee on Public Health Bill and Nuisances Removal Amendment Bill, Of which Committee you were the Chairman. I stated my opinion that certain useful though offensive trades do not cause, or in any way promote the prevalence and mortality of cholera, fevers, and other diseases, which are communicated from person to person, and which, on account of the property of being so communicated, take on very often the form of epidemics. I explained the grounds of my opinions as well as the opportunity permitted. Although I had published the same opinions on more than one previous occasion, and they had received no notice except of approval, I have been subjected since expressing them to the Select Committee to some[3/4] rather severe attacks, commencing in the newspaper press, and continued in the medical journals.

The writers of these attacks have assumed and asserted that the opinions I have expressed on the subject of offensive trades are altogether new and peculiar. This error might be excused in the editor of a newspaper, but in the editors of the two medical journals who have given a leader on my evidence it is altogether unpardonable. It is only necessary to quote the following passage from page 635 of Dr. Bancroft's work on Yellow Fever, published in 1811, in order to show that my opinions on this point are at all events not new.

"The following statement is extracted from a letter written to the author by Mr. Lawrence, Anatomical Demonstrator at St. Bartholomew's Hospital; whose character, talents, and professional acquirements, have already, at an early period of his life, greatly and justly advanced him on the road to eminence.

"'In a constant attendance at the dissecting room of St. Bartholomew's Hospital, for more than ten years, I have never seen any illness produced by the closest attention to anatomical pursuits, except such as might be expected to follow from a similar confinement and application to any other employment. 4/5]

"'When it is considered that most of the students come from the country, and that many spend much time in dissection, being employed also in writing, reading, etc., during the rest of the day, it will not be a matter of surprise that their health should occasionally suffer: but the indisposition has never appeared to derive any peculiar character from the exposure of the subject to putrid effluvia. Of course you will except from this observation, the effects which may arise from the absorption of noxious matter from wounds received in dissection. It has not appeared to me that ill consequences of that description follow more frequently from the dissection of the most putrid, than from that of recent bodies. The following particulars will afford the most complete proof, that the exhalations from decomposing animal substances are not necessarily injurious to the human body. John Gilmore, together with his wife, and two sons, lived for ten years in a room under the anatomical buildings of St. Bartholomew's Hospital. The whole family slept, as well as spent the day, in this apartment, which received a very small quantity of light, inconsequence of its single window opening against a high wall. The room was at the end of a passage, in which several tubs containing bones in a state of maceration were generally placed, and with which other divisions of the cellars communicated,[5/6] continuing large excavations for receiving the refuse of the anatomical rooms. The latter were not separated from the passage by any door.

"'The animal matters thrown into the receptacles last mentioned, are, I believe, converted into adipocere, and the fetor is consequently not so offensive as if they went through the putrefactive process; but the whole place was constantly filled with a close cadaverous smell, very disagreeable to any persons who went down from the fresh air. During the whole day, Gilmore was employed about the dissecting room, in removing the offals, in cleaning macerated bones; in short, in an almost constant handling of putrid matters. He always enjoyed good health, was fat, and possessed very great bodily strength. He left his situation in consequence of an apoplectic attack, and died lately, at the age of 69, after two other similar affections. His wife survives, enjoying a good state of health. Neither of his sons appears to have suffered from any unwholesomeness of their abode. They are both hearty and strong, although they have been employed some years in attending the dissecting room. But the whole family left the cellar soon after the father's first attack.'"

The above facts, detailed by Mr. Lawrence, agree with the experience of all medical men regarding [6/7] dissection, and the bearing of these facts on the mischief alleged to arise from other occupations connected with decomposing animal matters must be very evident. I could, indeed, if I had time, quote many passages from trustworthy authorities to prove that skin dressing, bone crushing, and other offensive trades are not perceptibly injurious to health; but I have preferred to select the above passage, because the experience and opinion of Mr. Lawrence, who is well known to you as an eminent member of the Medical Council of the General Board of Health, will naturally have more weight with you, than the opinions and evidence of others who might be strangers.

It is hardly necessary to remark that occupations which are not injurious to those who follow them, cannot, by any stretch of the imagination, be considered to do harm to those who merely live in the neighbourhood in which the occupations are pursued. As the gases given off from putrefying substances become diffused in the air, the quantity of them in a given

Space is inversely as the square of the distance. Thus, a man working with his face one yard from offensive substances, would breathe ten thousand times as much of the gases given off as a person living a hundred yards from the spot. Currents of air would make a difference; but this would be the average proportion of the gases inhaled respectively by the two [7/8] individuals. Therefore, if these gases are supposed to act as ordinary poisons, the health of the workman ought to be injured ten thousand times as much as that of the inhabitant a hundred yards from the factory; or if they are supposed to act as specific poisons, having the power of reproduction, so that the smallest quantity might suffice to set up disease, then the chances of contracting such disease would be ten thousand times greater amongst the workmen, than amongst those living at a distance of one hundred yards.

It is sometimes asserted that workmen become inured by habit to offensive trades, and thus escape the diseases which attack others at a distance; but they who use this argument forget that those at a distance ought by habit to become inured to their minute dose as well as the workmen to the larger quantity; and also that the workmen are not inured by habit when they first enter on their trades, and ought then to be affected by their occupation if it really produced fevers and other epidemic diseases; but this is contrary to experience.

The gases which result from the putrefaction of animal substances are capable of causing death, when they are breathed in a concentrated form, and it is often assumed that this of itself proves that they must be more or less injurious in the most minute quantities. This, however, by no means follows, for car-[8/9] bonic acid gas causes instant death when not much diluted, and yet it is a natural constituent of the atmosphere, and is constantly breathed in all parts of the world. Carbonic acid gas is not so powerful a poison as some of the gases resulting from putrefaction; but then the amount of it always present the air is far greater than that in which the gases from putrefying substances are ever met with in the streets and houses nearest to any kind of offensive factory.

The editors who have attacked me have apparently copied each other's sentiments, and they have assumed that my opinions respecting offensive trades are the consequence of the principles I have endeavoured to establish concerning the mode of communication of cholera, typhoid fever, and some other diseases. But this is an error, for I held the sentiments that I now hold respecting offensive trades, for many years before my opinions were formed, on the mode of communication of cholera, at the latter part of 1848; and in this respect I was in no way singular. One of the most approved and largely circulated works on the Practice of Physic, is Dr. Watson's Lectures, which appeared in the Medical Gazette in 1841-2. The following passage will show Dr. Watson's opinions with respect to the alleged connection between fever and offensive effluvia. [10/11]

"Again, continued fever has been attributed, with great confidence, to a vitiated state of the air, from the putrefaction of dead animal and vegetable substances. Dr. Bancroft deals with and demolishes this error also, showing that neither the putrid atmosphere of the dissecting-rooms (respecting which you must have some personal experience), nor the noisome effluvia from full and ill-conditioned burial grounds, nor those to which tallow-chandlers, soap-boilers, glue and catgut makers, and the melters of whale-blubber, are exposed, nor the foul air of sewers and privies, have ever been known to produce anything like continued fever. In some parts of Essex, near the coast, where the farmers are in the habit of manuring their fields with shoals of sprats, I have seen large tracts covered with these fish in a state of putrefaction. The stench they occasion is horrible; but no disease results. Dr. Chisholm, in a paper to which I can only refer, but which I would recommend you to look at, in the sixth volume of the Edinburgh Medical and Surgical Journal, brings forward other, and very satisfactory, instances, to the same purpose: from a bone manufactory, near Bitton, in Gloucestershire; from an establishment (now relinquished) on the banks of the Avon, for converting the flesh of dead animals into adipocere; from manufactories for refining sugar, where the blood of [10/11] slaughtered animals is kept for that use by butchers; from the leather-dressing business; all tending, I say, to the conclusion, that air, contaminated by the decomposition of animal substances, is not necessarily noxious to life; still less productive of that specific disease which we are now considering. The old belief, therefore, was unfounded, that the exhalations from the dead and putrefying bodies of men and horses, lying unburied on the field of battle, are capable of producing a pestilence. Many instances to the contrary are on record; one, of an early date, is thus stated by Diemerbroek:--'Anno 1642, in agro Juliacensi maxima strages facta est, et ad minimum 8,000 militum occisa fuerunt, præter majorem adhuc famulorum, etc., numerum: corpora inhumata sub dio computruerunt, nulla tamen pestis insecuta est.'"--Medical Gazette, 1842,, p.791.

Although there is sufficient direct evidence to prove that cholera is neither caused nor increased by offensive trades,* that circumstance is very much confirmed by the facts which I have been able to collect in illustration of the mode of propagation of cholera; for it is not reasonable to seek for addi-[11/12] tional causes of any phenomenon, when a real and adequate cause is known. Thus the itch, owing to its being almost exclusively confined to the poor and dirty, is more confined to neighbourhoods where offensive smells prevail, than typhoid fever is, and very much more so than cholera is; yet no one attributes the itch to the gases given off by decomposing animal or vegetable matters, for the simple reason that the real and sufficient cause of that complaint is known. (*The Registrar-General's sub-district of Lambeth Church, first part, which extends by the river side from Westminster Bridge to Vauxhall Bridge, and contains most of the manufactories that are [11/12] Complained of in Lambeth, suffered only a mortality of 29 persons in 10,000, in the epidemic of cholera in 1854, whilst the more genteel, open, and thinly peopled sub-districts of Clapham and Kennington, in which few factories are situated, suffered as follows: Clapham, 103; Kennington, first part, 125; and Kennington, second part,76 deaths from cholera to each 10,000 inhabitants. The sub-district of Saffron Hill, with the open Fleet Ditch flowing through it, and the slaughter-houses, knackers' yards, and cat-gut factories of Sharp's Alley, on its eastern boundary, suffered the lowest mortality from cholera in 1854 of any sub-district in London except one. The mortality of the Saffron Hill sub-district was only 5 in 10,000, whilst that of London altogether was 45, and that of the fashionable Belgrave sub-district was 60 in 10,000.)

It appeared to me that you were not sufficiently aware of the bearing that any facts, which should establish a distinct and adequate cause of cholera, would have on the alleged effect of offensive trades in promoting that malady; for when a member of the Select Committee--Mr. Wilkinson, I think--put a

question to me respecting the cause of the outbreak [12/13] of cholera near Golden-square, you did not allow it to be answered, although, undoubtedly, the late epidemic of cholera was the cause of the bills being framed which are now before Parliament.

The absence or defect of drainage, undoubtedly, assists very much in the propagation of many epidemic diseases, and as defective drainage very often occasions offensive smells, the editors of whom I complain have arrived at the short and easy conclusion that any trade or manufacture, which gives rise to an offensive odour, must also promote disease. The matters, which it is the purpose of drainage to remove, contain all that comes from the sick, as well as the healthy part of the community, and, when they are not properly removed, they permeate the ground, and pollute the pump-wells and other supplies of water and, in this way, as I have elsewhere adduced a good deal of evidence to prove,* several epidemic diseases may be propagated; the morbid matter of each disease reproducing its own specific malady. (*On the Mode of Communication of Cholera.) There are also other ways more gross and material than a mere odour, by which the absence of proper drainage aids in the spread of disease. On the other hand, occupations connected with the skins, bones, or fat of dead animals, cannot in any way assist in conveying[13/14] the morbid matter of disease from the sick to the healthy.

I am, of course, no defender of nuisances, but I consider that if a trade is more offensive than it ought to be, or is conducted in a place where it has no right to be, it might be proceeded against by the ordinary laws as a nuisance, without using the word pestiferous, or otherwise dragging in and distorting the science of medicine.

Some of the manufacturing processes which give rise to offensive smells, are not only a source of wealth in themselves, but are highly useful to agriculture. These are circumstances that would, at one time, have been thought worthy of consideration, but, however desirable it may be that commerce and agriculture should not be injured on mistaken grounds, it is still more important that the real causes which affect the health of the community should be ascertained, and that epidemics should not be attributed to a wrong cause, for I have previously shown that great increase of disease has several times been occasioned by presumed sanitary measures.

I have of course not written this letter in the way of personal complaint against the editors by whom I have been attacked. My reason for writing it is, that I have an impression that the editors in question [14/15] have really expressed the sentiments of the majority of the persons who have paid little attention to the subject, but are more likely to influence legislation than careful and industrious observers.

I have the honour to be, Sir,

Your obedient servant,

John Snow, M.D.

Sackville Street, July 12th, 1855.

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