Note: When Dalrymple’s long-running BMJ column ended in 2012, he had a backlog of about 60 unpublished pieces, and he kindly gave them to us to post here at Skeptical Doctor. We are posting them on Wednesdays to coincide with the schedule of his old BMJ column. We hope you enjoy them.

Every author, I suppose, is familiar with the experience of realising the mistakes he has made the very moment that what he has written has been committed irrevocably to print. And this was so with a book of mine published in 2012 titled The Policeman and the Brothel. I had overlooked something that should have been obvious to me, at least as a possibility.

My wife, who is a doctor, was doing a locum on the island of Jersey and I went with her. Finding myself with nothing to do there for three or four months, I researched three murders that took place there between December 1845 and February 1846, the last of them of a policeman called Le Cronier by a brothel-keeper called Madame Le Gendre, and wrote a book about them. Among other things I discovered in the course of my researches that about a half of all the newspaper proprietors or editors of provincial newspapers in Britain were also vendors of patent medicines, a case of commercial synergy, since patent manufacturers were by far the largest advertisers in their newspapers. And half of the advertisements were for remedies for syphilis, ergo… well, I don’t need to point out the moral.

One of the murders was by a man called Thomas Nicolle, the scion of a respectable family. Not sober, he went to a café in St Helier late at night, there had a quarrel with the owner over the cost of two bottles of champagne previously consumed by him (six shillings), and was thrown out by the owner who followed him and knocked him down in the street. Nicolle went back to his lodgings, fetched a gun, returned to the café and shot at random through the shutters, killing a man called Simon Abraham who was having a late night game of cards there.

Nicolle was sentenced to death, but his advocate went to London to obtain a reprieve from the Home Secretary, who granted it on the grounds that Nicolle had in the past been mad. I quote now what I wrote about some of the evidence at his trial:

According to [his landlady], his behaviour appeared strange and completely inexplicable on a number of occasions. For example she had seen him beating the walls with his fists until they bled… One night he slept in a box in his room instead of on his bed. [She] had never seen him drunk, and said that he was known… as Mad Nicolle.

At the time of his madness he was learning his trade which was that of… a hatter. Obviously, he was a mad hatter, but astonishingly and mortifyingly I missed this in my book. His symptoms, which fitted no commonly-seen pattern nowadays, were those of erethism caused by mercury poisoning. H A Waldron, in an article on the Mad Hatter in the BMJ in 1983, said the psychotic symptoms of erethism were excessive timidity, diffidence, increasing shyness, a desire to remain unobserved and an explosive loss of temper when criticised.

The treatment in those days was plenty of fresh air. Nicolle’s sentence was commuted to transportation for life to Van Diemen’s Land, where he presumably got plenty of fresh air. And it might have cured him, because he does not appear in the criminal records of Van Diemen’s Land or New Zealand, where he died.

How could I possibly have overlooked so obvious a diagnosis? But of course kind readers will point out that I have overlooked something in this article too.