You could make the argument that Oliver Sacks was of the last generation in which it was possible for a medical doctor to be a genuine polymath. Specialisation has tended to shut down the possibilities of wider speculation. In an interview in 2012, three years before his death at 82 from cancer, he suggested to me that he mourned the passing of the medical practice of telling the story of a life, as well as the progression of a disease, the way in which case histories were being eclipsed by “diagnostics, which causes doctors to simply tick off criteria without ever once describing a particular patient in detail”.

My life with Oliver Sacks: ‘He was the most unusual person I had ever known’ Read more

Sacks had particular reason to place his faith in the importance of thinking of a patient in all his or her possibility. The miracle of his application of the drug L-dopa to catatonic patients, described in Awakenings, was as much the result of his wider curiosity about consciousness, and his human tenderness, as his chance encounter with the chemistry of that drug in another context. The autobiography he completed just before his death revealed the roots of that humanity in a sort of Wordsworthian childhood wonder, a sense that he clung to and expanded throughout his scientific life. Along with that book, Sacks left instruction for this collection of essays to be issued after his death.

You can see why he did so. The essays – which dwell on his scientific heroes: Darwin, William James, Freud and others – locate him exactly and properly on the margins between experimental discovery and literature, head and heart. The delight of his meditation on Darwin and the Meaning of Flowers, the opening essay here, lies not only in its acute examination of evolutionary theory, but also in his love of Darwin’s method. In trying to understand how reproduction occurred in flowers, Darwin “painstakingly tried acting as a pollinator himself, lying face down on the lawn and transferring pollen” between primroses with different stigmas and styles before collecting the seeds to discover that the healthiest plants came from cross-bred varieties.

Oliver Sacks remembered by his nephew, Jonathan Sacks Read more

Sacks loves these details because he shared the excitement of them. He was desperate as a child – as Darwin had been – to observe a plant growing in real time, the way climbers set out tendrils as if they had eyes to find suitable support. He set up time-lapse cameras in his garden to watch how ferns unfurled “their tightly wound crosiers or fiddleheads, tense with contained time, like watchsprings with the future all rolled up in them”. He delights in Darwin’s obsessive efforts to anatomise the “mind” of earthworms, and Freud’s early drawings that proved the nerve cells in jellyfish and crayfish were basically similar to those of human beings.

Sacks’s enthusiasms are so finely and conversationally expressed as to be entirely seductive. Each essay contains a careful lifetime of observation and reading. His account of the action of false memory takes you from his own experiences – real and conjured – during the blitz to the Freudian “slippages and errors of memory that occur in everyday life” to the mysteries of unconscious plagiarism and borrowing in everyone from George Harrison to Helen Keller. His accumulated wisdom of our experience of time and consciousness, meanwhile, which the essays worry at and return to, makes a marvellous discrete series of meditations – and a profoundly moving one, since several of these pieces were written with the knowledge that his experience of both mysteries was soon coming to an end.

• The River of Consciousness by Oliver Sacks is published by Picador (£18.99). To order a copy for £13.15 go to guardianbookshop.com or call 0330 333 6846