Originally he only intended to collect skulls, Richard Harris explains mildly, as if a man could have no more modest ambition in life.
Somehow, though – after he acquired the lifesize Japanese skull complete with startlingly realistic serpent slithering through the eye sockets, Kiki Smith's bronze skull cast from her own head and inscribed with lines from Horace, and Robert Mapplethorpe's skull-handled walking stick photographed when the artist was dying of Aids – he kept going.
The collection, now on haunting display at the Wellcome Collection, grew to include a chandelier big enough for a cathedral, made entirely of plaster casts of bones (by the British artist Jodie Carey), photographs of medical students grinning over partially flayed corpses, anatomy textbooks, papier-mache skeletons from Mexico, medieval images of skeletons dragging lords, ladies, bishops and peasants into the Dance of Death.
Although London commuters need no reminding of mortality, anyone coming up from the underground into Euston station, opposite the Wellcome Collection, now passes a row of images of Edwardian postcards of buxom beauties and courting couples morphing into skulls, from the collection.
"It's a cracker, isn't it?" said Ken Arnold, head of public programmes, standing by John Isaac's lifesize sculpture perched on a packing case, a semi-dissected man with little remaining – both arms gone along with one leg and most of his skin – except his snarling anger. "When we had the Brains exhibition 12 people fainted. I wonder what it's going to be this time."
The Isaac is called "Are You Still Mad At Me?" Privately, the Wellcome staff call it "the breakfast-loser".
Arnold said the exhibition was a perfect fit for the Wellcome Collection, whose founder, Henry Wellcome, a more benign medications manufacturer, had a gigantic collection including mummies, shrunken heads, tattooed skin, Tibetan skull cups and a Chinese dentist's trade sign trailing strings of human teeth.
One very rare set of calendar sheets shows jolly skeletons smoking, drinking, playing music, and compounding medicines in a pharmacy. Curator Kate Forde points out drily in her caption: "Memento mori are rare in commercial advertising, which perpetually defers the future in order to emphasise the idea that you are what you have now." The skeletons were unusually accurate because they were drawn by a trained anatomist, and they also proved prophetic. The calendar was distributed to doctors in 1900 by the Antikamnia chemical company, which recommended its patients take two tablets every three hours for headaches, fever, insomnia or nervousness. The tablets, it was eventually established, were not only addictive but also toxic.
There are also works by major artists including Dürer and Rembrandt, and the Disasters of War engravings by Francisco Goya that inspired the Chapman Brothers to create modern horrors.
Harris, a retired antique prints dealer, only began collecting death objects and works a few years ago, selling a beloved collection of prints by Rembrandt, Picasso and Matisse to fund it. When his new treasures went on display earlier this year in Chicago, he thought he had 1,500 pieces. He believes he now has 2,000, but that could already be out of date: he is still commissioning new pieces, and acquiring old ones. One of the most arresting pieces in the show is one of his most recent purchases, a small wooden figure slumped on a battered wooden chair, a tomb guardian from the South Sea.
"Death has been a very important subject in art, and one that has meaning for all of us," Harris said. "All of these pieces stand in their own right as works of art, but if they persuade the public to engage with a subject too often kept at a distance, so much the better."
His wife of 45 years has been "very understanding", and his children just say "there goes Daddy again", he insisted. Unlike the many death-bed figures in the collection gazing hopefully towards heaven – or hopelessly in the case of the gouty 18th century man sprawled in an armchair, smashed wine bottle and glass by his side – Harris has no belief in an afterlife, and no interest in what happens to his own body after his death.
"I don't think the show is morbid," he said, slightly anxiously. "It's not a downer, I think it's quite uplifting."
• Death: A self-portrait, Wellcome Collection, London, free, until 24 February
