"On the prevention of cholera"

Medical Times and Gazette
(8 October 1853): 367-69
Article written/submitted on 27 September. A reprint was subsequently published (London: William Tyler, 1853)

By John Snow, M.D.

We cannot hope to prevent any disease unless we have a correct knowledge of its causes. As regards the cholera, many persons, indeed, consider that its causes are well-known, and also the means of its prevention; and they attribute its continued existence and extension entirely to neglect of the requisite measures for its suppression. Every candid observer must admit, however, that a great deal has been done within the last twenty years in the way of presumed sanitary improvement, much of it with the best results as regards the general health of the community, and all of it with the best intentions. Yet the cholera of 1849 was much more fatal than that of 1832, and now, on its third visit to our shores, it is prevailing to a more fatal extent in Newcastle than was ever before witnessed in this country. These circumstances clearly show, that the causes of cholera are not generally well understood, and that the true preventive measures have not been applied.

The first origin of cholera, like that of other epidemic disease, is hid in obscurity, and will probably remain so. It has been proved, however, by various documents quoted by Mr. Scot,* that cholera was prevalent at Madras in 1769, and that it carried off many thousands of persons at various places in the peninsula of India from that time to 1790. (*Report on the Epidemic Cholera. 1824. P.5.) From this period we have very little account of the disease till 1814, although, of course, it might exist in many parts of Asia without coming under the notice of Europeans. In June, 1814, the cholera appeared with great severity in the 1st Bat. 9th Regt. N.I. [Native Infantry], on its march from Jaulnah to Trichinopoly, while another battalion which accompanied it did not suffer, although it had been exposed to exactly the same circumstances, with one exception. Mr. Cruikshanks, who attended the cases, and made a report thereon, writes as follows:--

"It was the belief of the natives, strenuously fostered and inculcated by their spiritual guides, that the epidemic was the immediate consequence of the wrath of Heaven, outraged and insulted by the pollution of certain sacred tanks, situated at the village of Cunnatore, in which sepoys of low caste and camp followers had indiscriminately bathed. Such we may not regard as affording a very satisfactory solution of the difficulty; yet it leads, I think, directly to the true point of inquiry. At Cunnatore, the force was so encamped, that while the 5th Native Infantry on the right had their supplies of water from wells, the puckallies of the 9th Native Infantry procured water for that battalion from tanks situated on low ground on the left of the line. The fact, that the disease first broke forth in a day or two after passing Cunnatore; the prevailing opinion of the natives, that it originated there, and that somehow it was connected with the tanks; a desire to discover some one cause confined in its influence and operation to one out of the two battalions; lastly, the difficulty or impossibility of lighting on any other; all these led to inquiry, and to ascertaining with a considerable degree of certainty, that each battalion was supplied with water from a source distinct from the other."† (†Op. Cit. P. 237.) The cholera was said not be at Cunnatore at the time.

In 1817, the cholera prevailed with unusual virulence at several places in the delta of the Ganges; and, as it had not been previously seen by the medical men practising in that part of India, it was thought by them to be a new disease. At this time the cholera began to spread to an extent not before known; and, in the course of seven years, it reached eastward to China and the Philippine Islands, southward to the Mauritius and Bourbon, and to the north-west as far as Persia and Turkey. With its progress afterwards in Europe the reader is, no doubt, quite familiar. The cholera travels along the great tracks of human intercourse; it never attacks the crews of ships coming from a country free from cholera to one where the disease prevails till they have entered a port or had intercourse with the shore. Its exact progress from town to town and from country to country has not always been traced, but it has never appeared except where there has been ample opportunity for it to be conveyed by human intercourse. It is quite true, that personal communication cannot always be detected between the new cases and previous ones; but this is only what happens in small-pox, which is proved by inoculation to be a communicable disease. In an interesting account of an epidemic of variola at Corfu, Mr. Spencer Wells writes as follows:--"On the 27th of February, 1852, a case of small-pox occurred in the Jew's quarter at Corfu. Small-pox had been prevalent for some months on the opposite shores of Albania, which were only placed under a quarantine of observation of twenty-four hours. No communication could be traced between any infected person or object from Albania to account for the appearance of the disease in Corfu."‡ (‡ Medical Times, current vol., p. 83.) Innumerable instances are, however, observed of the communication of cholera by personal intercourse, and hundreds of them of the most convincing kind; as where the first case in a neighbourhood is that of a person newly arrived from a place where the disease was prevailing, and the next cases are those of members of his family or other who attend on him. There is, it is true, what has been considered the other side of the question. Numbers of persons come into near proximity with the sick without contracting the malady; but this only shows that it is not communicated either by contact with the patient or by effluvia given off into the surrounding air; and as there was no right to assume that these two modes, usually denominated contagion and infection, are the only ways in which disease can be transmitted from one person to another, the evidence of the communication of cholera remains unshaken to afford a full explanation of the progress of the disease; indeed, the only explanation of it that can be offered.

It only remains, then, that the mode in which cholera is communicated should be known, in order that the means of arresting its progress may be pointed out. Every disease communicated from one person to another is necessarily caused by some material proceeding from the former and received by the latter. Now, if cholera were one of those disorders which are ushered in by general symptoms, such as fever, we should have no indication of the channel by which the morbid poison is received, whether, for instance, by the alimentary canal, by the lungs, or in some other way, but should be left to determine this point by circumstances unconnected with the pathology of the disease. Cholera, however, always commences with disturbance of the functions of the alimentary canal; all the early symptoms are connected with this canal, and the effects which follow are only the result of what has occurred in it. The exudation of the watery part of the blood into the stomach and bowels causes the faintness and sinking. The blood which remains in the vessels, being too thick to pass readily through the capillaries, both the pulmonary and systemic circulation are impeded; hence the difficulty of breathing, the general coldness, and state of collapse. How far the cramps depend on irritation of the nerves of the alimentary canal, and how far on the want of fluidity and proper circulation of the blood is not very evident; but it is quite certain that they do not depend on any cholera poison circulating in the blood, for the cramps and all the symptoms of collapse disappear for a time on the injection of a weak saline solution into the veins, which merely replaces what has been lost by the bowels. It is evident from this circumstance that the blood is not poisoned in cholera, except in cases of secondary illness, when it becomes charged with urea and other excretory matters, owing to congestion of the kidneys. The primary and essential morbid actions of cholera being confined to the alimentary canal, it follows that the materies morbi of cholera must find access to it by being swallowed, that it must increase and multiply there, and be discharged to be a source of danger to others.

Before pointing out the precautions which these views [367/368] suggest, it will be well to examine what light they throw on the progress of cholera, and what confirmation they receive from general and particular facts connected with its history. It has been observed, in all parts of the world, that nothing assists the spread of cholera more than want of personal cleanliness. When we consider how free the evacuations from the stomach and bowels of cholera patients often are, both from colour and odour; how suddenly and copiously, and with what force they are generally discharged, it is evident that the hands, both of the patient and his attendants, are liable to be soiled with them. Unless great care is taken to wash the hands frequently, the more especially before taking food, or handling and preparing the food of others, small quantities of the evacuations must necessarily be accidentally swallowed. The influence of dirty habits in aiding the spread of cholera is thus clearly accounted for. It is analogous to what occurs among house-painters in regard to lead-poisoning. Those of cleanly habits escape; while others constantly swallow a little paint with their food, and become affected with colic. The scarcity of water, of course, is an obstacle to cleanliness, even when the inclination prevails; and this has been frequently observed to be connected with the unusual extension of cholera in a town or neighbourhood. The reason why Medical men, and other persons of cleanly habits, who do not stay to eat and drink in the sick room, are scarcely rendered more liable to cholera by their avocations, while it often fares differently with the social visiter, is perfectly explained by the above views. It is evident, also, why the Medical man can make inspections of the dead bodies of cholera patients with impunity; while they who wash and lay out the body often suffer. The Medical man is certain to wash his hands after his operation, while the persons who perform the other offices mentioned, especially among the poor, are almost as certain to neglect that duty. It is obvious that, where a whole family live, night and day, in one small room, in which the cooking is done and the meals are eaten, that the food is very liable to become contaminated, in the event of a case of cholera occurring; and, where several families live in one room, the risk amounts almost to a certainty. Now, under these circumstances, cholera is observed to spread through the family and household; while cases occurring among the well-to-do, who have separate kitchens and sleeping-rooms, are seldom observed to spread the disease. The great havoc which cholera has made in certain asylums for pauper children and pauper lunatics, to which it has gained access, is explained by the crowding which existed, and more particularly by the difficulty of maintaining cleanly habits among these classes of persons. On the other hand, the almost total escape of the inmates of the model lodging-houses in 1849, although inhabited by a class of persons who usually suffer more than others, was due to the excellent arrangements for cleanliness, and the proper separation of apartments and offices required for distinct purposes. About a month ago, certain German emigrants, on their way to America, who had crossed the sea from Hamburg and Rotterdam, where cholera was prevailing, to the port of Hull, and had gone thence by rail to Liverpool, were seized with cholera (some of them fatally) in the latter town; and it is most likely to the well-regulated Emigrant's Home, in which these cases occurred, that the town of Liverpool owes its present freedom from the epidemic.

The colliers of this country suffered much more from cholera than persons in any other occupation whatever, both in 1832 and 1849,--a circumstance which can only be explained by the mode of communication of the malady above pointed out. Pitmen are differently situated from every other class of workmen in many important particulars, as the following reply, which I received a few days ago from the agent to a colliery near Leads will show:--"Our colliers descend at five o'clock in the morning, to be ready for work at six and leave the pit at from one o'clock to half-past three. The average time spent in the pit is eight to nine hours. The pitmen all take down with them a supply of food, which consists of cake, with the addition, in some cases, of meat, and all have a bottle, containing about a quart of 'drink.' I fear that our colliers are no better than others as regards to cleanliness. The pit is one huge privy, and of course the men always take their victuals with unwashed hands." It is very evident, that when a pitman is attacked with cholera while at work, the disease has facilities for spreading among his fellow-labourers such as occur in no other occupation. That the men are occasionally attacked while at work I know, from having seen them brought up from some of the coal-pits in Northumberland in 1831-2, after having had profuse discharges from the stomach and bowels and while fast approaching to a state of collapse.

It is not only when the cholera evacuations are accidentally swallowed in small portions with the food that they have the power of propagating the disease, but also when they are diffused in a very large quantity of water. On former occasions* I adduced several instances in which a violent irruption of cholera in a limited community was caused by the contamination of the water of a well or tank by the contents of drains and cesspools, when there were cholera evacuations in the latter,--instances in which irruptions of cholera among greater numbers of people were connected with a similar contamination of the tidal ditches of Rotherhithe and Bermondsey,--and instances in which whole towns were, more or less, affected by drinking the water of rivers into which the sewers discharged their contents. It was shown that, in the latter case, more particularly when the water was distributed by water-works, the cholera, instead of creeping along in the back streets, and courts, and alleys, inhabited by the poor, became generally diffused among all classes of the community. (* Medical Gazette, 1849. Vol. II, pp. 730, 745, 923; and Medical Times, 1851. Vol. II, pp. 559, 610.) This circumstance has just received a fresh illustration at Newcastle and Gateshead.

The Water Company, formed about six years ago for the purpose of supplying these two towns with water from a rivulet and springs at Whittle Dean, about ten miles distant, have lately found their proper sources insufficient for the demands of the population and the various factories, and have been making use of the pipes of a former company to obtain water from the Tyne, at a spot about a mile above the towns. The tide, however, flows for several miles further, and, consequently, carries the sewage past the place where the water is obtained. When the cholera became established in Newcastle, in the early part of the present month, the sewers necessarily conveyed the peculiar evacuation of the disease into the river, and for some days the deaths from cholera increased in a geometrical ratio,--being, on the 13th, 29; 14th, 59; 15th, 101; and they increased in Gateshead in the same proportion. Complaints of the impure state of the water were now more loudly expressed than before; and on this day the Tyne water was discontinued, and the mortality no longer increased in the same frightful manner. It kept at this point, and even a little above it, for a few days, however, before it began to decrease, perhaps on account of impurities still remaining in the pipes and in the cisterns where the latter are used. Besides, it must be borne in mind, that the disease might maintain, by its ordinary means of propagation, the wide dominion it had obtained through the aid of the steam-engine and pipes of the Water Company. The cholera on this occasion has been very fatal among the genteel and well to do classes in all parts of Newcastle and Gateshead, as well as among the poor. Only a few streets in these towns are situated at a low level, for the banks rise very abruptly at a little distance from the river on both sides. A great portion of each town is elevated nearly 200 feet above the river, and some parts are nearly 300 feet high, yet the Water Company above mentioned supplies all these districts, and all have been visited severely by the cholera. The diminished mortality which is taking place now (September 27) is chiefly confined to the lower parts of the two towns. I have obtained the above particulars from a medical friend in Newcastle, and also from the published reports of the meetings of the Town Council and other public bodies.

In 1831-2 there were no waterworks in Newcastle. It was supplied in an insufficient manner with spring water, which generally had to be carried some distance to the houses from "pants" in the streets. The epidemic cholera was pretty severe at this time. In 1849 Newcastle and Gateshead were plentifully supplied with water unpolluted with sewage, by the Company above-named, who had then no occasion to have recourse to the Tyne. At this period these towns escaped with a very slight visitation from cholera. The existing epidemic, under the circumstances above narrated, has carried off more than six times as many persons in Newcastle during the first four weeks of its presence, as it carried off in a similar period in 1831-2; and more than twice as many in Gateshead. [368/369]

The absence or deficiency of drainage and the overflowing of cesspools promote the spread of cholera, as of typhoid fever, by permitting the evacuations of the patients and the water in which soiled linen has been washed to flow on the surface, and contaminate everybody who comes in contact with them; but the want of proper drainage is often still more injurious, by causing the liquids which ought to be carried off to saturate the ground, and percolate into the pump wells and other supplies of water.

The measures for the prevention of cholera which are suggested by the circumstances and views above detailed, may be divided into those which can be carried out in the presence of the epidemic, and those which, as they require time, should be taken beforehand.

The measures that should be adopted during the presence of cholera are:--

1st. To take care that there is a hand-basin, water, and towel, in every room where there is a cholera patient, and to take care that they are used by the nurse and other attendants, more particularly before touching any food.

2nd. To immerse the soiled linen of the patient and his bed in water as soon as it is removed, until such time as it can be washed, lest the evacuations should become dry, and be wafted about as a fine dust.

3rd. To take care that the water employed for drinking, cooking, and preparing food, (whether it comes from a pump-well, or is conveyed by pipes,) is not contaminated with the contents of cesspools, house-drains, or sewers; or, in the event that water free from suspicion cannot be obtained, to have it well boiled and, if possible, also filtered.

4th. When the cholera prevails very much in the neighbourhood, to have all the provisions which are brought into the house well washed with clean water, and exposed to a temperature of at least 212º Fahr., or to make them undergo at least one of these processes.

5th. When a case of cholera appears among persons living in a crowded room, the healthy should be removed to another apartment where it is practicable, leaving only those who are useful to wait on the sick.

6th. As it would not be practicable to clean out coal-pits and establish privies and lavatories in them, or even to provide the means of eating a meal with anything like common decency, when the cholera makes its appearance, the time of working should be divided into periods of four hours instead of eight, so that the pitman might go home to their meals, and be prevented from taking food in the mines.

The measures which can be taken beforehand to provide against a visitation of cholera, are,--

7th. To effect good and sufficient drainage.

8th. To provide the inhabitants with an ample supply of water, which is quite free from contamination with the contents of sewers, cesspools, and house-drains, or the refuse of people who navigate the rivers.

9th. To provide model lodging-houses for the vagrant class, and sufficient house-room for the poor generally.

10th. To inculcate habits of personal and domestic cleanliness among the people everywhere.

The advice and direction which are issued respecting cholera by authority, are directed almost entirely against dirt and nuisances; but, unfortunately, they are perfectly silent respecting that particular kind of dirt which does the mischief. The Board of Health directs its attention more particularly to offensive effluvia, as a supposed cause of cholera. When the ready means for the communication of this disease exist, it often happens, for very evident reasons, that offensive gases are not altogether absent; but it has been satisfactorily proved, that the effluvia arising from the decomposition of vegetable and animal matters have nothing whatever to do with cholera.

The communicability of cholera ought not to be disguised from the people under the idea that the knowledge of it would cause a panic, or occasion the sick to be deserted. English people would not desert their friends or relatives in illness, though they should incur danger by attending to them, but the truth is, that to look on cholera as a "catching" disease which one may generally avoid by a few simple precautions, is a much less discouraging opinion than that which supposes it to depend on some mysterious state of the atmosphere in which we are all of us immersed and obliged to breathe.

18, Sackville-street.