John Snow was the eldest of nine children, born to William and Frances (Fannie) Snow. The first 14 years was spent with his family in York before moving to Newcastle-upon-TYNE to take up a medical apprenticeship. On Snow’s baptism record, his father’s occupation is stated as a “laborer”, yet John Snow and several of his siblings obtained notable success in their lives in industry, teaching, clergy and medicine. His high intelligence is perhaps not unremarkable in a working class family of the 19th century, but what is most interesting is how they were able to raise themselves form the lowest level of non-royal British society-that is, level 5- to higher levels.
John Snow, his brother Thomas Vicar, was social class 1. William, a hotelkeeper, hatter, was level 2 and 3 depending on what part of his life you were viewing. His brother, Robert, was a collary, or mine secretary, level 2.
The family lived on North Street in York in the parish of All Saints, and this is an area within the old Roman city and along the river house. This was a busy, crowded area during Snow’s childhood because this was the center of commerce with houses right up to the stone jetties of North Street on the river house. North Street had been the trading center of this city since the 10th century. This was one of the poorer residential sections of York and subject to flooding-- poorly drained—and subject to epidemics of cholera and other disease states. The city suffered during the 1832 cholera epidemic, and this started along North Street. The North Street home had been the family residence over several generations. Snow’s father, William, married Fannie Epson, the illegitimate daughter of John Epson, who before his death mad her his natural daughter. In the early years of his marriage, he worked as a laborer in various businesses along North Street. This would include steam flourmills, flour warehouses and work of that nature. He then improved himself from a laborer to a driver of a horse-drawn vehicle, moving goods from ships to warehouses or from warehouse to warehouse. He soon improved his to and moved away from the river and bought a home and continued to have children. He subsequently bought a farm on the outskirts of York, improving his lot even more, and ended up owning that property and houses along Wellington Row, which was a few streets away form North Street where he had moved in 1823.
Religion was an important part of this family’s life. The Snow’s all attended All Saints’ Church of England, that parish church on N9orth Street, his mother and father were buried, there and all nine of their children were baptized there. It is very likely that the children attended the Sunday school at North Street. Schooling is the single most achievement of this family. It is clear that his mother and father were not illiterate, since they were able to sign various legal document, deeds, and birth certificates, etc. But their children seem to have bee highly educated and even though the father had a very low income, they somehow managed to promote hard work and diligence in their children and they were able to attend the schools in the area that were call4d private grammar schools that were supported by the church and various charities. It took sixpence a week to have your childe in a charity or private school and with eight children and an average income of 15 shillings per week as a driver; it is amazing that the parents were able to accomplish what they did with their children. John Snow learned Latin and Greek, which prepared him for entry into medical apprenticeship.
When William Snow, John’s father, became a farmer, he raised himself in the social status ladder. As stated a few moments ago, his brothers and sisters were also great achievers and this ability of intergeneration mobility in the 19th century in Britain was very rare indeed. Certainly to go from social class 5 to social class 1 was almost unheard of. The lives of their children reflect the characteristics of hard work, motivation and skill.
As mentioned earlier, it was unusual for 19th century London doctors to establish themselves, especially if they came from humble beginnings. John Snow’s training demonstrates what hard work and a keen mind could achieve in rural England and London in the min-19th century.
At age 14, Snow was taken on as an apprentice to William Hardcastle, the surgeon/apothecary in Newcastle-on-the-Tine. Hardcastle’s home and practice were on Westgate Street, opposite St.John’s Church, and he held the position of surgeon and secretary to the lying-in hospital in Rosemary Lane, a few minutes walk from his home. Snow spent five years with Hardcastle, as his apprentice, and part of this time gave medical service to the colliery in Killingworth at the time of the first cholera epidemic in 1832.
Why Snow chose this town of Newcastle and Dr. Hardcastle is unknown, although it is probably somehow related to his uncle, Charles Epson, the brother of his mother. Hardcastle himself had served an apprenticeship in the city of York, so he probably knew the family, although nothing is known for certain of a prior connection.
The clearest way in the 18th centuries for a person to rise from the lower class and climb the social scale was to become a physician. The cost, however, was considerable, but Snow was able to make the payments in tuition. The fee could very between five shillings and 500 pounds a year, depending on the city and notoriety of the senior doctor. There were additional expenses of medical books, instruments, lecture courses and hospital practice. It was a one-to-one relationship between master and pupil that had existed for almost 1,000 years in Europe and 1500 years if you go back to Greece. Basic knowledge of Greek and Latin were needed, and Snow had both of these. The apprentice acquired practical skills though daily contact with the master and though the training period attended formal lectures, either by the master or at other sites. The mandatory part of the apprenticeship by the mid-19th century was passing the examination of r the Society of Apothecaries in the Royal College of Surgeons. Snow too examinations in Latin, anatomy, physiology, and theory and practice of medicine, chemistry, botany and materia medica. He had a six-month hospital practice and nine months working in a dispensary. This system was under evaluation an evolution at the time Snow was training.
Snow studied diligently and took advantage of all the lectures and other educational opportunities in the Newcastle-on-the-Tine area. Snow assisted Hardcastel at the lying-in hospital and learned surgical and obstetric techniques at that time. His master was popular in medical circles, so Snow was well connected.
Snow studied at the Newcastle School of Medicine in the 1830’s and this mirrored the provincial medical schools, which were emerging in Manchester, Birmingham, Sheffield, Leeds and Liverpool at the time. London, of course, was the great center.
During his apprenticeship, Sow was exposed to the cholera epidemic in 1831 and 1832 as mentioned before. This, of course, started his thinking, which ultimately led to his great discovery.
In completion of his term with Hardcastle, Snow began a series of assistantships with various rural physicians. Eventually, through these connections, he was able to earn enough money to go to London to continue his training.
Snow was committed to two causes in his early life: vegetarianism and temperance. He first advocated a diet as a potential for relieving certain diseases as proposed by John Frank Newton, famous at the time for his writings and converted the poet Percy Bysshe Shelley to this diet. Snow initially included milk, eggs and butter in his diet, but after a while converted to a vegan diet. However, in 1845, he suffered symptoms of renal disorder and was persuaded to change his diet, and he improved by eating animal products. The Temperance Movement began in 1828 and Snow became a teetotaler in the early 30’s; however, later in life he drank a little wine with his dinner.
He arrived in London in 1836 and enrolled as a pupil at the Hunterian School of Medicine in Great Windmill Street. The great Wiliam Hunter had established this since 1746-almost 100 years before in Covet Garden. This school had been famous for 100 years. Snow paid for a series of lectures and this introduced him to the upper echelons of English medicine and eventually for his induction into the Royal College of Surgeons- the highest board rating that a physician could have. He achieved this at a rather early age.
His lodgings were situated less than a quarter of a mile from the Hunterian Western School and just a mile form Westminster hospital, where he also practiced medicine. He spent all his time studying medicine in one form or another: reading dissecting and attending the full range of lectures including chemistry, given at the Hunterian School. This culminated his academic experience. Then entered the Westminster Hospital for six months of surgical practice in 1837. This hospital had been founded in 1719 for the care of the sick and poor and was one of London’s leading teaching hospitals. There were several great surgeons there, and he watched all of them perform.
Hospital clinical teaching was just evolving at this time and was a great source of revenue for the leading surgeons and physicians, but the training itself was somewhat informal and great deal relied on the student’s energies and Snow had all the attributed needed to succeed. He passed his Royal College of Physicians examinations as well as apothecary examinations and in 1844, was Licentiate of the Royal College of Physicians-the highest award that one could attain.
Snow chose to remain in London to set up practice. This was somewhat difficult to do and it took several years to build a practice, so most physicians who stayed in London and did contract work at sick clubs and hospital dispensaries were some to the lowest paid doctors, but it allowed him to pay his bills and continue to build his practice. Over 90% of the physicians trained in London went back to small towns.
For years, Snow continued to grow. He attended lectures. He was hardworking and contributed to medical debates. Between 1837 and 1846, he wrote a host of papers discussing his important cases. He invented an instrument of paracentesis of the thorax and pessary of the sponge. Of the total of 1480 general practitioners listed in the medical directory of London in 1845, less than 8% listed any publications at all and Snow had five papers in various journals and a host of other reports.
Snow entered medicine during this window of opportunity and through his broad-based training with much clinical work, with particular experience in obstetrics and cholera; he was ready for his great two successes. To enhance his private practice, he began to sub-specialize in anesthesia. This allowed him to enter the next level o his career with a significant specialty in an overcrowded marketplace of general practitioners.
We will only spend a few moments discussing his anesthesiology career, because our main focus today is epidemiology. John Snow is one of the few physicians who were pioneers in two different fields of medicine-namely, anesthesia and epidemiology.
We are indebted to Benjamin Ward Richardson, a close friend of Snow’s, who left us the memoirs of John Snow, that were completed after his death in 1858 and again, a second edition in 1887. From this, we know much of what ultimately has been written about Snow. Richardson himself had a long and distinguished career in the history of medicine, having compiled The Asclepia- 11 volumes of essays on the science, art and literature of medicine, printed between 1884 and 1895. It was Richardson who completed Snow’s monumental work on anesthesia some two months after his friend died. The book was almost completed when Snow expired. The title of this book was On Chloroform and Other Anesthetics. The memoir that Benjamin Richardson wrote of Snow is still the best available source of information on Snow.
The royal College of Physicians in London has acquired the three casebooks of John Snow’s anesthesia material. In this he documents the cases of his general practice in anesthesia I, but nothing directly related to his epidemiological work on cholera.
Anesthesia began in the United States. It was first used by the dentist William Tomas Green Morton, who on 30 September 1846, administered sulfuric ether for dental extraction in his own practice. Two weeks later, he gave the first public demonstration of ether for surgery. This demonstration established anesthesia for the entire worked. It took place in Boston at the Massachusetts General Hospital 16 October, 1846- just over two weeks after his initial dental case. Morton attempted to gain financial advantage for himself and conceal the true nature of ether. This secrecy created a repugnant feeling among physicians and the public and he was much vilified for attempting to restrict the use for humanitarian discovery and for him to profit financially. Morton’s reputation was not the only casualty of this unfortunate approach, but it led to a much-muted reaction to the introduction of ether in the United States. Bostonians of 1846 could only inform their influential friends in Franc and outside America. The French looked upon this with some disdain, but the English reacted positively. It wasn’t long until on Saturday, the 19th of December 1846, that English dentist James Robinson administered ether to one of his patients in his office. Robinson appreciated the significance of Morton’s discovery and for several weeks promoted the agent. However, it wasn’t until Snow became interested after a few weeks that the anesthesia took on a scientific demeanor. Robinson used only empirical techniques, and some times the anesthetic gas ineffective. But Snow developed inhalation equipment and was able to produce results time after time on a regular basis. He also studied gas physiology, circulation physiology and soon figured out the basic principles of anesthesia that remain to this day.
In 1847, he published his small but classic textbook on ether anesthesia. He wrote several pamphlets and articles on the subject. He kept his casebooks and he soon realized that there would be other agents that would be of value and developed chloroform.
It took Snow only about four weeks of study to establish the principles of inhalation anesthesia that are used even to this day. Within a very short period of time, all the major surgeons in London began to use anesthesia-even those who first had doubted it, including the great Liston, who was a leading surgeon of London in this day.
Snow administered anesthesia for surgeons in many hospitals around London, in the offices of dentists and in his own office. He had and extremely busy practice. He was able with the income form this practice to purchase a better home and raise his standard of living. His notoriety and success was established when he gave chloroform to Queen Victoria during her last two labors.
Snow’s scientific insight was due to the theory that cholera is communicated by mean of contaminated water supply. His essay “Upon the Mode of Communication of Cholera”, which was first published in 1849, was interestingly enough rewarded a prize by the Institute of France, but was essentially neglected in his native land. In 1855, a second edition was published with a more elaborate investigation of the effect of the water supply of certain districts of South London in the epidemic of 1854.
By the middle of the 19th century, Soho had become an unsanitary place of cowsheds, animal droppings, slaughterhouses, grease-boiling dens and primitive, decaying sewers. Underneath the floorboards of the crowded cellars lurked something even worse- a fetid sear of cesspits, as old as the houses, and many of which had never been drained. It was only a matter of time before this hidden, festering time bomb exploded. It finally did so in the summer of 1854.
When a wave of Asiatic cholera first hit England in 1831, it was thought to be spread by miasma in the atmosphere. By the time of the Soho outbreak 23 years later, the medical knowledge had scarcely changed, although one man, Dr John Snow, the physician and anesthesiologist who became a pioneer in the science of epidemiology, had published a report speculation it was spread by contaminated water. Neither the authorities nor the rest of the medical profession had much truck with his idea. Cholera broke out four times between 1831 and 1854.nothing whatsoever was done to contain it, and it rampaged through the industrial cities of England, where tens of thousands of people died. It was the Soho area that suffered a few isolated cases in August, and then on the night of August 31, what Dr. now later called the most terrible outbreak of cholera whichever occurred in the Kingdom broke out. It was as violent as it was sudden. In the next three days, 127 people living in and around Broad Street died. Few families, rich or poor, were spared the loss of at least one member. Within a week, 75% of the residents had fled from their homes, leaving their shops shuttered, their houses locked and the streets deserted. It was like the Great Plague of the 17th century all over again.
By 10 September, the number of fatal attacks had reached 500 and the death rate in and around Golden Square had risen to 12.8 %- more than double that for the rest of London. Snow lived close by on Fifth Street and studied this outbreak very intensely. He had always felt like the disturbance began in the alimentary canal and was spread by poison passed from victim to victim through sewage-tainted water. The water companies of London, not surprisingly, were reluctant to believe this. Now he saw a chance to prove his theories linking the Soho outbreak to a single source of polluted water. He patrolled the district, interviewing the families of victims, and soon found that the pump on the corner of Broad and Cambridge Streets was at the epicenter of the epidemic.
Dr. Snow took a sample o water from the pump and on examining it under the microscope; he found that it contained “white, flocculent particles”. He was convinced that these were the source of the infection and he took his findings to the Board of Guardians of the St. James Parish, in whose area the pump fell. They were reluctant to believe him, but in the end, removed the handle form the pump as he requested. The cholera epidemic dramatically stopped.
By the end of September, 616 Sohoites were dead, but Snow’s theories were yet to be proved. There were several unexplained deaths from cholera that did not at first appear to be linked to the Broad Street pump water. A widow living in West Hampstead had died of cholera on 2 September, and her niece who lived in Islington had succumbed to the same symptoms the following day. Since neither of these women had been near Soho for a long time, Dr. Snow rode up to Hampstead to interview the widow’s son. He discovered from him that the widow had once loved on Broad Street and he had liked the taste of the well water there so much that he had sent her servant down to Soho every day to bring back a large bottle of it for her by cart. The last bottle of water, which her niece had also drunk from, had been fetched on 31 August at the very start of the Soho epidemic.
There were other factors that led Snow to isolate the cause of the cholera to Broad Street pump. For instance, of the 530 in mates of the Poland Street Workhouse, which was only around the corner, only five people contracted Cholera, but no one form the workhouse drank Broad Street pump water- they had their own well. The 70 workers in a Broad Street brewery, where the men were given and allowance for free beer every day and so never drank water from the pump, found no fatalities.
Still no one believed Snow. A report by the Board of Health a few months later dismissed his suggestions that the real cause lay in the general use of one particular well in the middle of the district and having its waters contaminated by the rice water evacuations of cholera patients. After careful inquiry, the report concluded, “We see no reason to adopt this view.” The Board was influenced strongly by the scientific theory of the day of miasma as the cause that was transmitted in the air. A Reverend Whitehead was a 29-year-old clergyman in the parish where Soho was located. He felt that this was the divine intervention of God – this horrible epidemic – but did some research on his own and showed that his distribution of cases was similar to Snow’s. To his credit, after reading Snow’s report and the two men having become quite familiar with each other, he admitted that it was not divine act of God, but that Snow’s theory was accurate.
I went to the Extrom Library and read in detail reports form the London Times about Snow and Whitehead and various vestry committees and Board of Health reports. In addition, I have found the obituary of Whitehead – a most interesting man. He is an important figure in Victorian England.
How do we make sense of all this? Why take time to discuss John Snow? Well, first of all, it is clear that he was the Father of Modern Epidemiology, but hid fundamental contribution in addition to his scientific approach and his deductive reasoning, rather than inductive reasoning, lies in many ways in the presentation of his data.
Snow was the first man that understood medical geography. I thought that he was really the original user of this dot map, but this is not the case. I am not certain if this is the original use of such medical geography techniques of presenting data, but in my research for this paper, I read all the material in the Kornhauser Rare Books Library on cholera during this period. There is a book entitled The History of Cholera in Exter in 1832 and a map virtually identical to the technique used by Snow is included in this book. I have never seen this map referred to in any of the bibliographies of the large number of articles I consulted about Snow. The implication is that he was the originator of this technique, but that is certainly not the case. Whether the book I quote is the only other source, I am not certain, but it is certainly the earliest I have seen.
Now I’ll spend a moment on Snow’s medical geography. Several papers have been written on this subject and they all point out the significance of his dot pointing on the maps. The most interesting fact that I found is that the English have essentially neglected his findings, and it was first in the Netherlands and finally the Germans in the third quarter of the e19th century, who began to really study Snow’s technique, commented on it, and began to re-examine this method of presenting data and the concept of medical geography.
We need to take a few moments to discuss the concept of miasma and transmission of contagion. The insight of John Snow is critical. In 1854, the cholera epidemic investigations included a local study of the Broad Street outbreak by Snow and an investigation of the entire epidemic undertaken by England’s general Board of Health. This was more than a quarter century prior to Koch’ description of the vibriocomma organisms. The Board of Health investigators saw microscopic vibriones in the rice water stools of cholera patients that in his later life concluded had been cholera bacilli. Although this finding was potential evidence for Snow’s views that cholera was due to contagious and probably live agent transmitted in the water supply, the Board of Health rejected Snow’s conclusion. The Board of Health amassed a huge amount of information, with several hundred charts and graphs, which were interpreted as supportive of the conclusion that the epidemic was attributable not so much to water as to air. Snow, by contrast, systematically tested his hypothesis that cholera was waterborne by exploring evidence that at first glance ran contrary to his expectations. Snow’s success provided support for a hypothetical/deductive approach in epidemiology, based on tightly focused hypothesis, strongly grounded in pathophysiology and not using the inductive approach-a reasoning prevalent at the time.
A brief paragraph from the report of the Committee on Scientific Inquiries in relation to the cholera epidemic of 1854 states, “Either in air or water, it seems probable that the infection can grow. Often it is not easy to say which of these media may have been the chief source of poisonous fermentation; for the impurity of one commonly implies the impurity of both; and in considerable parts of the metropolis (where the cholera has severely raged), there is a rivalry of foulness between the two.”
Books have been written on the concept of miasma and the purification and breakdown of organic material that got into the air and caused these epidemics. For those of you in epidemiology who might be interested, I would refer you to the work of W.H. Frost, the United States epidemiologist in the 1930’s, who was influential in reviewing the Dutch, German and United Kingdom literature and revived the work of John Snow.
I have tried to give an overview of this remarkable physician, anesthesiologist and epidemiologist, to show how, with careful study ad a prudent hypothesis, he was able to use modern scientific method to gradually develop his thesis and prove his point. Even though the authorities at the time were using inductive reasoning and the past theory of miasma, John Snow of course ultimately wins out.
But the irony of all this is that John Snow in some was got it all wrong.
The conclusion of this will make two important points. First of all, although Snow go it right in terms of his hypothesis and inductive reasoning, the epidemic was beginning to subside when he took the handle off the pump. The epidemic probably was shortened by the fact that 75% of the people left the area within a week.
So, did taking the handle off of the pump cure the epidemic? Well, it certainly prevented any further cases, if there was still cholera lingering in the well water. It was shown that the cesspool next to the well wall had broken down and eroded into the well, so we really don’t know for certain. However, Snow’s major contribution other than the idea of waterborne infection is his method of presentation, and this will be the last portion of this talk.
The material I speak of for the next few minutes is from, in my opinion, a very important book: Visual Expectations – Edie R. Fief. This publication is used by medical epidemiologists and processors of civil engineering and actually almost applies to virtually every field. I am going to show how Snow’s very graphic ad simple explanation made his proof more readily understood and interpreted. Also, a map from the Napoleonic Wars, showing Napoleon’s invasion of Russia and his retreat, and on the other had a very poor graphic demonstration that cost the American people tens of millions of dollars and the lives of seven of our most brilliant astronauts. The Challenger 51 flight crew died because of the simple misinterpretation of data that had been collected about the O ring that controlled the injection of fuel. It had been shown in experiments that this ring froze because of the liquid fuel and that it had a very good chance of causing an aborted mission and explosion. The problem was that those who did the experiments did not present the data in a way that they were interpreted properly, and the shuttle committee arrived at the wrong conclusion. I recommend this book to anyone who is doing epidemiology and making presentations of complicated material.
In the last two years, several editorials have appeared in the American Journal of Epidemiology, discussing John Snow and modern-day environmental epidemiology. The same issues Snow faced with the political authorities ad the powers-that-be exist today. Epidemiology studies are often very difficult to perform and certainly to control all the variables. The real John Snow was a man with a hypothesis, a theory that he put to rigid testing, and arrived at the right conclusion – and this several decades before Robert Koch isolated the vibrio cholera organism. These editorials point out that technological advances are making possible a wide range of new studies, designs, and strategies to better access both exposures and outcomes. Although the progress has been made, research in environmental epidemiology is far from perfect. The epidemiologist faces pressures and criticism from industry, regulatory bodies, and other scientific disciplines. It is important not to lose sight of the lessons from John Snow.
My final thought is that I would refer everyone to a recent editorial in the New England Journal of Medicine, 24 May 2001, entitled “The Powerful Placebo and the Wizard of Oz.”