John Snow and Waterborne Diseases

John Snow, M.D.: Early Career

John Snow: "Autotype from a presentation portrait, 1856, and autograph facsimile." Credit for both image and caption, Wellcome Library, London.

Little wonder that John Snow (1813-1858), the doctor who discovered how cholera was transmitted and thrust his findings in the face of a disbelieving medical establishment, should have become one of the heroes of medical science. A farmer's son from the north, who trekked all the way to the great metropolis to (eventually) become its saviour, his story is the very stuff of legend. Even by today's more measured assessment, he remains a towering figure, especially in the fields of epidemiology and public health.

Born in York, John Snow was the son of a Yorkshire labourer who later became a relatively well-to-do farmer. The youth was apprenticed at fourteen to an enlightened and well-connected Newcastle surgeon, William Hardcastle, who was on the staff of Newcastle's Lying-In Hospital. He first came up against cholera when it swept through the nearby West Moor colliery, a few miles from town by the village of Killingworth. This was during the epidemic of 1831-32. But at the time when cholera broke out again in 1846 Snow was in London. Having travelled to London on foot in 1836, Snow had now completed not just his apprenticeship but a thorough all-round training, including surgical practice at Westminster Hospital. In 1838 he had moved to Soho, opening a practice in Frith Street there, and also attending out-patients at Charing Cross Hospital, only a short distance away. He had subsequently earned medical degrees at the University of London (now University College, London), which had its medical facilities at University College Hospital. In 1845 he had become a lecturer in forensic medicine at the short-lived Aldersgate School of Medicine — though a large part of his experience had been in obstetrics, and his early interest was in the resuscitation of still-born infants, he also had a specialised knowledge of lead poisoning. Besides, in whatever he had undertaken, he had proved himself a keen and cutting-edge investigator. By the late 1840s he was best known for his research into anaesthesia, having published a groundbreaking study, On the Inhalation of the Vapour of Ether in Surgical Operations, in 1848.

Dr Snow's Early Investigations into Cholera

Snow had been a high-minded young man, a vegetarian as well as a teetotaller. In his more mature years, he was still a man of integrity, evincing "a complete lack of acquisitiveness and personal ambition" (Hempel 106). A bachelor, he was wedded to his work, endlessly painstaking in it, and dedicated to his scientific and humanitarian pursuits. On the theoretical level, he had approached the subject of anaesthetics from many different angles, from looking at the properties of the gas itself to studying its physiological and psychological effects. He had followed his findings right through to the practical stage as well, working out and designing the best means of administration. He had tested his inhalers in animal experiments, and had not shrunk from testing them on himself (see Johnson 65-68). Armed with his understanding of the operation of gases, when he again found himself treating cholera cases in his neighbourhood, he was not inclined simply to accept the prevailing "miasmic" orthodoxy. Moreover, he was prepared to follow unusual routes to establish his own theory. These ranged from reading accounts of the previous epidemic and examining current cases to consulting chemists, water suppliers and sewer authorities (see Johnson 71-74). By these means he worked out to his own satisfaction that the disease was spread not by touch, not through the air, but by ingestion. As he himself put it: "The morbid material producing cholera must be introduced into the alimentary canal — must in fact be swallowed accidentally, for persons would not take it intentionally" (Snow, On the Mode of Communication, 15).

Left: "Monster Soup, being a correct representation of that precious stuff doled out to us." A coloured etching by William Heath (1795-1840), 1828. Credit: Wellcome Library, London. Microscopic demonstrations had become popular at this time, but a woman drops her cup of tea in horror when she realises what Thames water might contain. Ironically for the present subject, a tiny figure in the left-hand corner doffs his hat to a water pump, supposedly a source of cleaner water. Right: A Punch illustration, in an article of 1850 entitled "The Water Kings," shows a boy shrinking away from the glass of water offered by Old Father Thames, who has his other hand on a tap (Vol. 18, p.62).

In an overcrowded city, with only the most primitive provisions for disposing of human waste, the finger pointed at contaminated water. In 1849 Snow published what should have been another groundbreaking paper, On the Mode of Communication of Cholera, demonstrating that more people died from cholera in the area served by certain South London water companies. These drew their water straight from the River Thames, which, at this time, had around sixty sewage outlets gushing into it (White 51).

The Reception of Dr Snow's Theory

Everyone knew the disgusting state of the Thames. Chadwick's insistence on removing human waste from cellars, and running it into the current drainage system, had only made it worse, as had the growing popularity of water closets. However, Snow's paper failed to make as much impression as the smell of the river itself. Another doctor, who still favoured the widely-held miasmic theory of contaminated air, wrote in the same year,

That cholera is produced by a specific poison is generally admitted by writers upon the subject. As to the essential nature of this specific miasm we are entirely ignorant; and we do not think it would serve any useful purpose to enter into a discussion upon the various hypotheses which have been proposed. For the most part the explanation offered to account for the mode of action of any one miasm will not cover the whole question; and this, in our opinion, is a fatal objection, for it is obvious that they present but one problem; and the true solution, when it comes, will explain all the varieties of the phenomenon. (Russell 122)

Others discussed Snow's hypothesis but mistrusted it: "At present these opinions of Dr Snow's can be considered only ingenious speculation," said one (Bushnan 33).

The Broad Street Pump

Left to right: (a) John Snow's house in Sackville Street, off Piccadilly (since demolished), with a plaque describing him as "physician and specialist anaesthetist who discovered that cholera is water-borne." (b) Snow's map of the area that provided the best evidence for his theory, around the Broad Street pump. Broad (now Broadwick) Street, W1, is the street that runs diagonally across the middle. Here, the black bars merge to denote houses where people died of the disease. These stand alongside the pump on the corner with Cambridge Street (now Lexington Street). (c) Silhouette of the pump indicating its original location. A replica has now been placed nearby. Credit for all three images: Wellcome Library, London. 

Snow, who was nothing if not tenacious, now set out to provide precise evidence in support of his theory. This time, supported by another local doctor and vestryman Edwin Lankester, and at street-level by local clergyman Henry Whitehead, he focused his investigation on the Broad Street area of Soho. Using statistics acquired from the General Register Office, he was able to demonstrate graphically that an unusual number of the 1853-54 fatalities had occurred among those drinking water from the pump there. The map on which he charted these fatalities was not the first to highlight clusters of a disease. But, after showing it to the Epidemiological Society in December 1854, he made a significant modification. Around the black bars representing the houses where deaths had occurred, he drew a line indicating closeness by foot to the pump. The uneven line, following the street pattern, made it clear that this was not a case of simply breathing in the air around the pump. He was also able to demonstrate that those who lived nearby, but drank from different sources (such as the local brewery's pipeline), had been spared. Finally, Whitehead did him a signal service by helping uncover the original source of the contamination: from talking to a bereft mother, he learnt that contaminated water had been thrown into a nearby cesspool. This proved to have leaked its virulent contents into the water source. As Lankester would say later, "the evidence adduced [in the revised monograph pf 1855] was most circumstantial and conclusive" . Though the epidemic was dying out by then, the parish Board of Guardians agreed to remove the pump handle so that people could no longer use it.

Reception of the Revised Edition of Dr Snow's Monograph

Snow seemed to have presented an open and shut case for his theory that the dreaded disease was passed on, as he was now able to formulate it, by the mixture of cholera evacuations with the water used for drinking and culinary purposes, either by permeating the ground, or getting into wells, or by running along channels and sewers into the rivers from which entire towns are sometimes supplied with water.

Whitehead had certainly been convinced, Lankester perhaps less so at that time. But at any rate the Board of Guardians had acted on Snow's findings. In the eyes of the medical establishment, however, the jury was still out. "This mode of conveyance was so novel that when first suggested it was almost universally opposed," said Lankester, adding "not a member of his own profession, not an individual in the parish believed that Dr Snow was right" (30-31; 34-35). Opponents of the theory continued to insist that there were other outbreaks that it failed to cover. They still preferred to blame "the atmosphere or its concomitant imponderable agents" (Acland 77). The Lancet criticised Snow savagely in its issue of 26 June 1858: "The fact is, that the well whence Dr Snow draws all sanitary truth is the main sewer. His secus, or den, is a drain" (qtd. in Johnson 205). Even in 1861, Mrs Beeton's specifics against cholera were "cleanliness, sobriety and judicious ventilation" (1073), not clean drinking water. Florence Nightingale, who nursed so many cases of the disease in the Crimea, remained a "convinced miasmatist" all her long life.

John Tenniel's famous cartoon, in the Punch of 10 June 1858 (facing p.17), shows a skeleton rowing along the Thames, with dead creatures floating alongside, and St Paul's, beloved symbol of the city and its spiritual life, in the distance. The Thames was still "a river of death" at this time, and the remedy involved a heavy financial commitment — hence the sub-caption, "Your MONEY or your LIFE!"

However, once he was thoroughly convinced, Lankester became a formidable ally to the cause. Appointed the first medical officer of health for Westminster in 1856, he was "a born publicist, teacher and reformer" (English). When The Lancet finally came round in 1866, it heaped praise on Snow as a "great public benefactor" who had "enabled us to meet and combat the disease" (qtd. in Johnson 213). At this time too, the last outbreak of cholera convinced William Farr, the superintendent of statistics at the General Register Office, that Snow had been right, and that water was, if not the only, then at least the most important, vehicle of the infection: he found that almost all those recently affected were getting their water from a part of the river not yet properly served by Joseph (later Sir Joseph) Bazalgette's new sewerage system. Though Farr never quite gave up his own belief that environmental factors were involved as well (see Eyler 230), this allowed social science to align itself more securely with Snow's detective work.
The Italian anatomist Filippo Pacini had already discovered the agent that caused cholera by then. When Robert Koch isolated it in 1883, and gained publicity for his findings, the last piece of the puzzle fell into place. Vibrio cholerae thrives in an aquatic environment — and inside human intestines. The accuracy of Snow's finding, and its full implications, could now be properly appreciated.

Dr Snow's Death and Reputation

Left: Equipment for the use of ether as an anaesthetic. Credit: Wellcome Library, London. Snow's pioneering work in this area was more widely recognised in his own lifetime. Right: Snow's grave in Brompton Cemetery, with a replica headstone replacing the one that was destroyed in an air-raid during the last World War (photograph by the present author).

In his final decade, Snow achieved eminence as an anaesthetist, attending Queen Victoria in her last two childbirths, in 1853 and 1857. On the first occasion, he and his colleagues had been criticised in the ever-sceptical Lancet (see "Anesthesia and the Queen"), but by the second, the queen's own endorsement had made the practice acceptable. However, Snow had a stroke in the following year, while preparing his latest work, On Chloroform and Other Anaesthetics (1858), for publication. He was found to have had underlying health problems, which his experiments on himself, not to mention the opposition to his ideas about cholera, might well have exacerbated.

Thanks to that opposition, Snow's epidemiological discovery did not produce any immediate, dramatic effect. The much-celebrated removal of the handle on the Broad Street pump came late in the Soho outbreak, after the source of the initial contamination had gone. The pump was in use again a few weeks later. The most pressing incentive for the firing ahead with London's new sewerage system was to get rid of the smell rising from the Thames, rather than any infective agent within it — during the "Great Stink" of 1858, the stench from the water had become completely unbearable. In general, admirable and appealing as Snow's story is, there is a tendency these days to put it in perspective. Careful mention is made of William Budd (1811-1880), another doctor working on the waterborne theory (though he himself gave Snow the "priority," and still made more of contamination through the air — see Snow, "On the Mode of Communication"). There are even questions about the way Snow presented his findings. Might not a "comparative, numerical argument" have been "more persuasive than the analytic approach employed by Snow" (Koch and Denike 1250)

Nevertheless, John Snow is still a very important figure in the history of epidemiology. The Broad Street episode is seen, appropriately enough, as a "watershed event," significant not simply because it proved Edwin Chadwick and the many other miasmatists to be wrong, but also because it showed that an epidemic could be tackled by practical intervention. It marks "the first time in history when a reasonable person might have surveyed the state of urban life and come to the conclusion that cities would someday become great conquerors of disease" (Johnson 235). The fact that hardly any "reasonable person" did appreciate this at the time is an important part of the story — the story of one man's doggged search for an answer, and persistence in trying to convince others that he had found it. This story has a life of its own outside the annals of medical science. Snow's greatest achievement may be in encouraging us to confront the problems that face the world today, and to have the courage of our own convictions, so that we too can help secure a viable way of life for future generations.