London was the centre of the world in 1850, but also a pit of filth and disease. Overcrowded and without a complete sewerage system, people living in areas that are today central and exclusive used to throw their waste into the street or into the River Thames. The continuous outbreaks of cholera also plagued the London populace until John Snow managed to find the connection between these two events, although he had to risk his prestige as an eminent doctor in Victorian England to do so. His great success helped to tear down the scientific theories of the day about infections and marked the birth of modern epidemiology.
During his childhood, he himself had suffered from the squalid sanitary conditions in the rapidly growing cities in the throes of the Industrial Revolution. The son of a coal worker, John Snow (15 March 1813 – 16 June 1858) was born in one of the poorest neighbourhoods in the city of York and was the first of nine children. As a child, he was noted for his mathematical skills and in 1827, at the age of 14, he became an apprentice to a surgeon and apothecary in Newcastle. He combined this post with studies at a newly established medical school; it was then that he had his first contact with cholera, during the second cholera pandemic, which came to Europe from Asia. Snow began investigating these epidemic outbreaks, working with surgeon Thomas M. Greenhow.
After a decade of schooling and medical experience, in 1836 John Snow moved to London to finally study medicine at the university. The following year, he began an internship at Westminster Hospital, where he stood out for his sense of observation: during his night shift, he designed experiments to study the origin of the diseases that so affected the students who performed autopsies at the hospital. He found that the common cause was poisoning from the arsenic fumes used to preserve bodies. That changed the practice of anatomical dissections and ended the use of arsenic in candle making.
An apprentice that became Queen Victoria’s surgeon
In 1844 he was finally able to complete his studies, add the title of doctor to his name and open a practice in the nowadays vibrant London borough of Soho. Dr. Snow gained prestige by applying scientific experiments to demonstrate the validity of his medical innovations, especially in relation to anesthesia. This new technique to avoid pain in operations and deliveries was still very unsafe, due to the lack of precise knowledge of the properties of the substances used as anaesthetics. Snow was one of the first to learn how to calculate the proper doses of chloroform and ether; he also designed devices and masks to apply them safely to patients and wrote a medical guide for their use. His renown was such that he was chosen to personally administer chloroform to Queen Victoria during the birth of her penultimate son, Leopold, in 1853. This contributed to the public acceptance of anesthesia.
However, John Snow is remembered today for another achievement, which put his reputation as a doctor in jeopardy, right when he was at the pinnacle of his career. During his long years as an apprentice and student, he had been taught the miasma theory: the “bad airs” that caused infectious diseases such as cholera or bubonic plague, according to the consensus of the scholars of the day. But there was something about this theory that did not make sense to Snow. He thought that if cholera was caused by harmful fumes, patients would exhibit some kind of respiratory symptom, which they did not. In addition, during the 1849 outbreaks, he conducted a case study and found that the incidence and death rate was much higher in South London, where the waters of the Thames were much more polluted than those drunk by the inhabitants of the rest of the British capital. In his article On the Mode of Communication of Cholera, he concluded that the cause was “morbid matter” invisible to the human eye, which patients ingested and which caused severe diarrhoea.
That hypothesis, which today is pure common sense, was then a challenge to established knowledge. Since the theory that microbes cause infections had not yet prevailed, Snow could not explain what this invisible and infectious matter was —just as Austrian physician and scientist Ignaz Semmelweis could not explain why doctors had to wash their hands to avoid spreading diseases from one patient to another.
A convincing proof that was not enough
Without being able to resort to his experimental demonstrations, the opportunity to act came in 1854 when a new and more serious cholera epidemic struck the United Kingdom. John Snow thoroughly investigated each case, talking to the sick and their families and pinpointing them on a map of London, searching for a correlation with the places from which the patients had obtained their drinking water. He was able to identify a water pump on Broad Street as the source of the outbreak in the Soho neighbourhood. His map of cholera convinced local authorities that this public water source had to be closed, and the number of cases began to drop dramatically.
For the success of that large-scale test, John Snow is remembered today as the founder of modern epidemiology. But at the time it was not enough. Despite the evidence, public health experts believed in the miasma theory, and the handle of the water pump was reinstalled, just as the neighbours demanded —a measure Snow fought until he died of a stroke in 1858, at age 45.
The facts proved him right in the decades following his death: during the next cholera epidemic (in 1866), health authorities proved that Snow’s ideas were valid and that the water from that pump was mixed with faecal water; in 1884 Robert Koch finally identified the faecal bacterium Vibrio cholerae as the agent causing cholera. A few years earlier, Louis Pasteur’s experiments had already shown that microbes were the cause of infections and also explained why brewery workers had remained immune to the 1854 outbreak around that Broad Street water pump. Fearful of that water, they drank only beer (produced from boiled water). These days, on a corner of that London street, one finds that same water pump, the John Snow Pub and a commemorative plaque placed in memory of Snow’s great scientific achievement.
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