Carefully, he unbound the linen and revealed to us a large hole in his breast, about the size of a Pippin apple, in the depths of which, as I leaned forward to look more closely at it, I saw a pink and moist fleshy substance, moving all the time with a regular pulse.

"See?" exclaimed Pearce, the heat of whose excited body seemed to fill the room with a tropical dampness. "See it retract and thrust out again? We are witnessing a living, beating heart!"

The man smiled and nodded. "Yes," he said. "A fracture of my ribs, occasioned by a fall from my horse two years ago, was brought to a terrible suppuration, voiding such a quantity of putrefaction that my doctors feared it would never heal. It did, however. You can see the sconce of the old ulcer at the edge of the hole here. But its ravages were so deep as to expose the organ beneath."

I was dumbfounded. To observe, in a living being, standing nonchalantly by a fire, as if about to welcome friends for a few rounds of Bezique, the systole and diastole of his heart affected me profoundly. I began to understand why Pearce was in such a lather of excitement. But then – and this is why I set down the incident as a possible beginning to the story now unfolding round me – Pearce produced a shilling from the greasy leather purse in which he kept his pitiful worldly income and gave it to the stranger, and the man took it and said: "You may touch it if you wish."

I let Pearce go first. I saw his thin, white hand creep forwards and tremblingly enter the thoracic cavity. The man remained still and smiling. He didn't flinch. "You may," he said to Pearce, "put your hand around the heart and exert gentle pressure."

Pearce's thin mouth dropped open. Then he swallowed and withdrew his hand. "I cannot do that, Sir," he stammered.

"Then perhaps your friend will?" said the man.

I rolled back the lace at my wrist. Now, my own hand was shaking. I remembered that, just prior to Pearce's appearance in my room, I had cast two pieces of coal onto my fire and hadn't washed my hands since, but only wiped them carelessly on the seat of my breeches. I examined my palm for coal dust.

It was faintly smudged with grey. I licked it and rubbed it again on my velvet buttocks. The open-hearted man watched me with an utter lack of concern. At my elbow, Pearce, in his vaporous dampness, was breathing irritatingly through his mouth.

My hand entered the cavity. I opened my fingers and, with the same care I had applied, as a boy, to the stealing of eggs from birds' nests, took hold of the heart. Still, the man showed no sign of pain. Fractionally, I tightened my grip. The beat remained strong and regular. I was about to withdraw my hand when the stranger said: "Are you touching the organ, Sir?"

"Yes," I said, "don't you feel the pressure of my fingers?"

"No. I feel nothing at all."

Pearce's breathing, at my side, was rasping, like that of a hounded rodent. A pearl of sweat teetered on the tip of his pink nose. And my own mind was now forced to contemplate an astounding phenomenon: I am encircling a human heart, a living human heart with my hand. I am now, in fact, squeezing it with controlled but not negligible force. And the man suffers no pain whatsoever.

Ergo, the organ we call the heart and which is defined, in our human consciousness, as the seat – or even deified as the throne – of all powerful emotion, from unbearable sorrow to ecstatic love, is in itself utterly without feeling.

I withdrew my hand. I felt as full of trouble as my poor Quaker friend, to whom I would have turned for a tot of brandy, except that I knew he never had any. So while our visitor calmly strapped on his linen pad and his steel plate and stooped to pick up his shirt, Pearce and I sat down on his extremely hard settle and were, for a good few minutes, devoid of words.

From that day, I was unable to have the same reverence for my own heart as other men have for theirs.

3. My father was appointed glovemaker to the restored King in January 1661.

I was by then at the Royal College of Physicians, after four years at Padua, studying under the great anatomist, Fabricius. I was at work on a paper entitled, "The Footsteps of Disease: a Discussion of the Importance of the Seats of Tumours and Other Malign Diversities in the Recognition and Treatment of Illness." But I was becoming lazy. Several mornings a week, I would sleep late at my lodgings, instead of attending, as I was pledged to do, the Poor Sick of St Thomas's. Several afternoons, I would walk in Hyde Park, with the purpose only of snaffling and leading to what I call the Act of Oblivion with some plump whore – when I should have been at lectures.

The truth is that, when the King returned, it was as if self-discipline and drudgery had exploded in a clap of laughter. I became much too excited by and greedy for life to spend much of it at work. Women were cheaper than claret, so I drank women. My thirst for them was, for a time, unquenchable. I tumbled them riotously. Two at a time, I longed to take them, immodestly, like the wild hogs whose hair my own spare locks resemble. In public places even: in the night alleyways, in a hackney coach, on a river barge, in the Pit of the Duke's Playhouse. I dreamed of them. Until the day I went to Whitehall. And after that day – so extraordinary and unforgettable was the impression it made upon me – I started to dream about the King.

Admiration for craft and skill is, I now understand, at the root of the generous but stubborn nature of King Charles II. He took my father into his service because he recognised in him the dedicated, skilled and single-minded craftsman. Such people delight him because they inhabit an orderly, meticulously defined world and never aspire to cross over into any other. The haberdasher, my father, never considered for one moment becoming, say, a gardener, a gunsmith or a moneylender. He laid out a precise territory with his skill and kept within it. And King Charles, while trying on a pair of my father's exquisitely moulded kid gloves, revealed to him that this was how he hoped the English people would behave during his reign, "each," he said, "in his appointed station, profession, calling or trade. And all contented in them, so there is no jostling and bobbing about and no one getting above himself. In this way, we shall have peace, and I will be able to rule."

I don't know how my father answered him, but I do know that it was on this occasion that the King promised, "at some future time, when you are bringing me gloves", to show my father the collection of clocks and watches he kept in his private Study.

No doubt my father bowed humbly. Very few people ever enter the King's Study. The only key is kept by his personal servant, Chiffinch. And it was at this moment – on his knees, perhaps? – that my father spoke up for me and asked the King whether he could bring his only son, from the Royal College of Physicians, to make his acquaintance, "in case His Majesty should ever have need of an additional physician in his household… a physician for the People of the Bedchamber, perhaps, or even for the scullery boys…"

"By all means," it seems the King replied, "and we will show him the clocks, too. As an anatomist, I expect he will be interested in their mechanical complexity."

So, on a November afternoon, with a chill wind blowing him forward up Ludgate Hill, my father arrived at my lodgings. I was, as had become my habit on a Tuesday, engaged in the Act of Oblivion with the wife of a ferryman called Rosie Pierpoint. Her laugh was as rich and juicy as that part of her anatomy she coyly referred to as her Thing. Encircled both by the Thing and the laughter, I was giggling ecstatically and bumping so energetically towards my brief Paradise, that I didn't see or hear my father as he entered my room. I must have been a risible sight: my breeches and stockings still tangled round my ankles, the sandy hogs' hair that sprouts in the crease of my bottom unflatteringly visible, Mrs Pierpoint's legs flailing either side of my back, like a circus tumbler's. I blush to remember that my own father saw me like this and, when he was consumed by fire a year later, I had, in the midst of great sorrow, the cheering thought that at least this memory burned with his poor brain.