On a cold winter's morning in 1878, medical students gathered in a gas-lit operating theatre where a long wooden table stood ready. As Joseph Bell, Edinburgh Royal Infirmary's senior surgeon, entered the room, the hubbub died away.
To the relief of some of the younger attendees, there would be no surgery today: instead, Bell was about to give a demonstration of the incredible deductive skills which earned him his nickname, 'the demon of diagnosis'.
The surgeon took his seat as the patient was ushered in. Bell pressed the tips of his slender fingers together and narrowed his piercing grey eyes as he carefully studied the clothes, mannerisms and features of the man.
'Of course, gentlemen,' he said, breaking the silence stifling the room, 'he has been a soldier in a Highland regiment'.
Bell then pointed out confidently that the man's short stature meant he was probably a bandsman, and that the swagger in his walk suggested someone who played the bagpipes.
Once he had shared his assessment, he turned his attention back to the visitor, who – to Bell's surprise – contradicted him, insisting that he was merely a shoemaker with no military background.
Certain that his assessment was correct, Bell ordered two assistants to take hold of the patient and strip him to the waist. Sure enough, a lie was uncovered.
Basil Rathbone as Sherlock Holmes in the Adventures of Sherlock Holmes that was released in 1939
Joseph Bell, the genius surgeon who taught Conan Doyle at Edinburgh University, inspired the literary character
Tattooed on the man's chest was a telltale letter D – the man was a deserter. Bell's students were transfixed; none more so than a thickset young man with a bushy moustache.
Seated at the front of the audience, as always, Arthur Conan Doyle absorbed the details of every feat performed by the man who, in time, would inspire him to create the beloved fictional detective Sherlock Holmes.
For Bell, every patient was a text to be studied, and he took particular pleasure in inferring facts about a person's life and occupation, even when such knowledge had little immediate clinical value.
A pinprick-speckled forefinger betrayed a tailor. A worn area on the inside of the knee of a man's trousers revealed a cobbler who hammered out leather on a stone resting against his leg.
'Nearly every handicraft writes its sign-manual on the hands,' he explained. 'The scars of the miner differ from those of the quarryman. The carpenter's callosities are not those of the mason.'
Bell's way of thinking about medicine – as a science of reading signs – was what captivated Conan Doyle. It showed him that diagnosis and detection required largely identical skills – skills used to supreme effect by Holmes, Bell's fictional counterpart.
Since his first appearance in print in late 1887, and the 59 tales of his adventures penned subsequently, Sherlock Holmes has become the most iconic fictional detective of all time.
Depicted in film and television more than 250 times – clad in a deerstalker hat and tweed cape, while clutching a pipe and a magnifying glass – Holmes holds the Guinness world record for the most portrayed literary human character in history.
To have been the inspiration for that creation might seem flattering. But, as we will see, the more popular Holmes became, the more the comparisons began to plague Bell. And similarly, Conan Doyle would struggle to escape the fictional protagonist who might never have existed were it not for his medical mentor.
Bell, who came from a long line of doctors, was described by colleagues as a distinctive character. A 'thin, wiry, dark' man, he had suffered a serious case of the bacterial infection diphtheria, which affects the throat and had the lasting effect of raising the pitch of his voice.
This characteristic was inherited by Holmes who, according to his friend and confidant Dr Watson, spoke in 'high, somewhat strident tones'.
Bell and Holmes also shared a disregard for officers of the law, the former opining that 'the fatal mistake which the ordinary policeman makes' was that 'he gets his theory first and then makes the facts fit it'.
Like Holmes, Bell believed that there was nothing worse than a lazy, disorderly mind. But the detective's cold and unemotional personality was a product of the author's imagination.
Whereas Holmes remained a bachelor, Bell was a family man whose beloved wife Edith died soon after giving birth to a stillborn son in 1874, leaving him with three children under the age of ten.
He never remarried or fully recovered from the loss of Edith. But, whatever his personal suffering, he cultivated a professional approach that was always ordered and logical. And it is not surprising that this quality appealed to someone from Conan Doyle's chaotic background.
The eldest of nine children, Arthur Doyle (Conan was one of his middle names) was born in 1859, in a humble dwelling near Edinburgh's city centre. His father Charles was an unsuccessful artist whose alcohol abuse sank the family into debt.
The Doyles lived precariously, moving frequently into ever-cheaper lodgings where Charles's desperation to get his hands on drink saw him selling their bed linen, raiding the children's money-boxes and even drinking furniture varnish when he couldn't afford alcohol.
Charles was eventually placed in a home for 'intemperate gentlemen' and, as poverty tightened its grip on the growing household, Conan Doyle turned to a career in medicine to bring his family some financial stability. He started his medical studies at the University of Edinburgh in 1876.
After he began taking the extracurricular class in diagnosis which Bell taught at the Royal Infirmary, Conan Doyle was chosen to be his outpatient clerk – taking the histories of as many as 80 patients a day before showing them into the large room in which Bell sat in state, making his diagnoses.
'He often learned more of the patients by a few quick glances than I had done by my questions,' remembered Conan Doyle.
'Did you like your walk over the links [golf course] today as you came in from the south side of town?' Bell asked an Irishman ushered into the amphitheatre.
'Yes, did your honour see me?' the man replied with surprise.
Bell had not, but he had noted the reddish clay on the man's boots. 'There is no such clay anywhere else around the town for miles,' he declared. Conan Doyle would recycle this moment of deductive genius in his second Holmes novel, The Sign Of Four.
On another occasion, a young doctor determined that a patient with a limp was suffering from a disease of the hip, and Bell immediately scoffed: 'Hip – nothing!'
He went on: 'Observe closely. There are slits, cut by a knife,
in those parts of the shoes where the pressure is greatest against the foot. The man is a sufferer from corns, gentlemen.'
But Bell instinctively knew the patient had not come to the hospital to seek help for his feet. 'This is a case of chronic alcoholism,' he said. 'The rubicund nose, the puffed, bloated face, the bloodshot eyes... all show this.
'In this instance my diagnosis is confirmed by my seeing the neck of a whisky bottle protruding from the patient's right coat pocket.'
Bell would say his methods were really quite 'elementary' – a favourite phrase. But they resonated with Conan Doyle who, after graduating in the summer of 1881, set up in private practice in Portsmouth.
A keen writer, even as a student, he had already been selling short stories to supplement his income, a need that became even greater in 1885 when he married his first wife, Louise Hawkins, the sister of a patient.
With a spouse and soon two children to support, he turned to writing detective fiction – until then a kind of cheap entertainment in which the investigator often broke a case only when some random piece of information fell into his lap.
Conan Doyle was determined to build a different kind of tale – one in which the detective's success depended on method, analysis and the careful weighing of evidence. And when he looked for a model of such intellectual acuity, his imagination turned back to his old professor.
Beyond his roles as doctor and educator, Bell was also a formidable forensic expert who testified at many trials, including one in which he worked alongside a cantankerous authority on ballistics named Dr Watson.
Since Conan Doyle had taken one of Watson's courses at the Royal Infirmary, there is speculation that Holmes's trusted companion was based loosely on him.
Far more certain is the influence on Conan Doyle exerted by Bell's close associate Sir Henry Duncan Littlejohn. As Edinburgh's eminent police surgeon, Littlejohn was a pioneer of fingerprinting and crime-scene photography.
He and Bell collaborated on many cases in the Scottish capital, including one featuring a charming but murderous Frenchman named Eugene Chantrelle. His hidden depravity later inspired Robert Louis Stevenson, another Edinburgh resident, to write his novella Strange Case Of Dr Jekyll And Mr Hyde.
The real-life Dr Jekyll had subjected his young wife Lizzie to repeated physical and emotional abuse before taking out an insurance policy on her life. Then, at the beginning of 1878, he slipped a fatal dose of opium into her lemonade, knowing that it left behind few traces in the body.
He might have escaped the hangman had not Littlejohn thought to examine the vomit stains on Lizzie's nightdress in which he discovered opium. He then scoured the city's pharmacies until he found the one where Chantrelle had bought an unusually large quantity of the drug.
Like Bell, Littlejohn gave lectures at the Royal Infirmary during Conan Doyle's time there as a student. He illustrated these with macabre objects garnered from crime scenes he had attended, including daggers, pistols, skulls, and a glass jar containing a man's thigh preserved in spirits and still bearing the 'fearful gash' which had killed him.
While Bell gifted Holmes his incisive mind, Littlejohn gave him his world, offering a real-life template of crime and detection upon which Conan Doyle could build his popular fiction.
And popular it certainly was. Following the publication of the first Holmes adventure, A Study In Scarlet, in December 1887, sales of the stories on both sides of the Atlantic soared beyond anyone's wildest imaginings, and a fictional titan was born.
So much so that by 1891, having written five Holmes tales, Conan Doyle was worrying about the effect they were having on his parallel career as a historical novelist.
'I was in danger of… being entirely identified with what I regarded as a lower stratum of literary achievement,' he lamented. No matter what Conan Doyle did, he struggled to be seen as more than just the creator of Holmes, and soon Bell would come to feel that he too was living in the detective's shadow.
That he had inspired the character was known to only a handful of people until an 1892 newspaper interview, in which Conan Doyle described him as 'the man who suggested Sherlock Holmes to me'.
With characteristic modesty, Bell resisted the comparisons. 'Doyle's the clever man,' he insisted. 'It's nothing to do with me.'
But thereafter he was hounded by newspapermen and began to resent the shattering of his privacy. Worse still, he felt that Holmes eclipsed his own identity, reducing a lifetime of work to a gimmick of fiction. 'I am haunted by my double,' he told a friend.
In 1893, Conan Doyle attempted to kill Holmes off in The Final Problem – the story in which he and his nemesis Professor Moriarty engage in hand-to-hand combat at Switzerland's Reichenbach Falls, before both plunge into the abyss.
When it was published, it was rumoured that Londoners were donning black armbands, and letters from distraught and angry readers started arriving at Conan Doyle's door. One began 'You brute!' and an irate woman was said to have struck the author with her handbag on the street.
After a decade of intense public pressure, and faced with tempting financial offers from publishers, Conan Doyle finally gave in and resurrected Holmes in The Hound Of The Baskervilles. He presented this as an earlier and previously untold adventure which allowed the detective to prowl the story's fog-bound moors and solve a mystery once again, without having to fudge the apparent finality of his demise.
Sherlock Holmes, it seemed, could not be killed. But the man who had inspired him was growing weak with age. In October 1911, Bell died of heart failure at the age of 73.
In death, as in life, the world saw him through the lens of Conan Doyle's most famous creation, with newspaper obituaries regaling readers with stories of his almost preternatural powers of deduction, and underscoring the link to Holmes.
By then, Conan Doyle's wife Louise had died of tuberculosis and in 1907 he had married Jean Leckie, with whom he had three more children. They were together until Conan Doyle's death from a heart attack in 1930, aged 71. Holmes, of course, has outlived both his creator and the man who inspired him. The great detective has been reinvented countless times, but his trademark analytical brain and devastating logic are always present.
Bell might be long gone, but through Holmes, his methods – and a trace of his voice – still captivate us today.
Adapted from Sleuth-Hound by Lindsey Fitzharris, to be published by Allen Lane on Tuesday, priced £25. To order a copy for £22.50 (offer valid to November 1; UK p&p free on orders over £25) go to www.mailshop.co.uk/books or call 020 3176 2937.