He began his long and transcendent career in a nondescript laboratory on the Adriatic Sea, dissecting eels.
He examined hundreds of the animals, working long hours amid stench and slime, peering through a microscope at countless tissue samples, in search of an organ that had eluded earlier anatomists — male testicles.
"Since eels do not keep diaries," the investigator, 19-year-old Sigmund Freud, wrote to a friend in the spring of 1876, the only way to determine gender was to cut and slice, "but in vain, all the eels which I cut open are of the fairer sex."
He ended the letter by sketching an eel, swimming through the text, its face fixed with a slight, Mona Lisa smile.
Beginning May 11, the New York Academy of Medicine will exhibit the largest collection of Freud's drawings ever assembled, including several pieces from private collectors that have not been displayed in public. The drawings, some embedded in letters and scientific essays, chart the evolution of the Austrian neurologist's thinking, from his early and lesser-known devotion to marine anatomy to the psychological theory that would alter forever humans' conception of themselves and launch a discipline, psychoanalysis, that dominated psychiatry for half a century. The American Psychoanalytic Association and the New York Psychoanalytic Society and Institute collaborated in the exhibition.
Freud's methods have fallen from favor in recent decades, but science historians say that his investigation of the unconscious more than a century ago stands as a revolutionary achievement that still informs many therapists' understanding of memory, trauma and behavior.
The exhibit is one of many events being held around the world this spring to commemorate the 150th anniversary of Freud's birth, May 6, 1856. These include scholarly lectures, conferences and films, as well as lighter fare, like "On the Couch: Cartoons from The New Yorker," at the Museum of the City of New York, running through July 23.
Freud's drawings were serious science, the eel doodle notwithstanding. In the latter part of the 19th century, German researchers considered drawing to be instrumental to scientific discovery, both as a way to capture the microscopic detail of nerve cells, for example, and to illustrate theories of how the brain might work, said Lynn Gamwell, the curator of the exhibit and the director of the Art Museum at the State University of New York at Binghamton. "Einstein once said that when he thought about science, he thought visually, he thought in pictures, and this appears to be the case with Freud," said Dr. Gamwell, a professor of science history.
Freud's drawings tell a story in three acts, from biology to psychology, from the microscope to the couch. The first, from Freud's college years into his mid-20's, took place in laboratories, where he examined the nervous systems of crayfish and lamprey, among other animals. The 21 drawings from this period would look familiar to anyone who used a microscope in high school, but on closer inspection betray compulsive detail.
One, titled, "On the structure of the nerve fibers and nerve cells of the river crayfish," depicts four types of nerve cells and minutely details the elements in the nuclei, the cell bodies shaded so carefully that they appear three-dimensional, alive, alien eyeballs bobbing in space.
In another sketch, of the spinal anatomy of the lamprey, nerve fibers braid together like climbing vines, with cells hung throughout like clusters of ripening grapes.
These are the work of someone who loved the laboratory, scholars say, and who seemed to invest even his earliest efforts with a sense of importance, a conviction that he was about to break something big.
"That is the way Freud's mind worked," wrote Ernest Jones, a disciple of Freud's, in his 1953 biography, "The Life and Work of Sigmund Freud."
"When he got hold of a simple but significant fact he would feel, and know, that it was an example of something general or universal," Dr. Jones wrote.
By his late 20's, Freud had gained some experience with patients and, in a second phase of his career, he began to focus on brain function rather than descriptive anatomy.
One drawing from this period, meant to illustrate the brain's auditory system, is as spare and geometric as a Calder sculpture, with fibers running between neural regions. The sketch is meant to represent specific pathways in the brain, but the depiction is dramatically more abstract than his earlier work.
In another, from an unpublished essay titled, "Introduction to Neuropathology," looping lines connect several nodes in a diagram intended to show how areas of the brain represent the body, arms, face, hands.
"It is no exaggeration to say that this insight is the precise point at which the mind — that aspect of the organism which represents the body not concretely but rather functionally, abstractly and symbolically — entered Freud's scientific work," Mark Solms wrote in a commentary that accompanies the drawings.
Dr. Solms, a psychoanalyst and professor of neuropsychology at the University of Cape Town, translated the works from the original German.
At the time these drawings appeared, many neurologists presumed the body was somehow mirrored in the brain, perhaps altered in form but recognizable, intact.
Yet in this sketch and others like it, Freud said the brain worked differently, that its fibers and cells "contain the body periphery in the same way as a poem contains the alphabet, in a complete rearrangement," based on a body part's function, not its location, Dr. Solms writes. Later research supported Freud's conception.
To capture what was running through the young scientist's own mind in this period, the mid-1880's, might require a Goya or a Lucian Freud, an artist familiar with longing and euphoria, frustration and deep anxiety. For Freud was in love, engaged in a tumultuous courtship with Martha Bernays of Vienna, complete with feuds with her mother and brother. He was experimenting with cocaine, on himself and on others, for a variety of mental and physical ailments, with increasingly disastrous results. And he was consumed by anxieties about his purpose, his scientific future and, most of all, his income.
Full-time research appointments were hard to secure at the time, especially for Jews, and Freud's scientific work provided very little income. He was desperately trying to raise money to pay for his wedding.
"He started taking in patients out of economic necessity," said Dr. Charles Brenner, a psychoanalyst and the author of "An Elementary Textbook of Psychoanalysis."
"Had he had a rich father, or not been a Jew, he would have stayed in the lab for the rest of his days," Dr. Brenner said. "But because he had to treat patients with psychogenic illnesses, it forced him to keep searching for treatments to help him in his own work."
This part of Freud's career — the third phase, — has become as familiar as Einstein's thought experiments with the streetcar or Darwin's ruminations on finches.
Freud became fascinated by the case of a young German woman, known to history as Anna O., a colleague's patient. Anna O. suffered from debilitating hallucinations and paralysis that dissipated when she talked about the symptoms.
Freud experimented with this "talking cure" and found it soothed several of his own patients who were suffering from similar psychosomatic symptoms, then called hysteria.
From 1892 to 1895, he refined his therapy to include free association, encouraging patients to trace the threads of their memory, back to when their symptoms first surfaced, and beyond, to earliest childhood. On these excavations, and in his self-analysis, Freud gathered the evidence on which he built his famous theory of the basic geography of the psyche: the primal id, the rational ego and the censorious superego.
He continued drawing diagrams to illustrate his findings. The first purely psychoanalytic drawing, Dr. Solms said, appeared in an 1894 letter from Freud to his friend and colleague, Dr. Wilhelm Fleiss. The style is reminiscent of earlier sketches — looping lines connecting nodes — but the nodes now represent psychological processes like memory, not physical locations in the brain.
A few years later, the diagrams become much more abstract: A sketch from 1900 illustrating the mental processes involved in dreaming looks like a bar graph.
A diagram completed in 1898, "The Psychical Mechanism of Forgetfulness," resembles the schematic for an air-conditioning system, complete with arrows and boxes.
But by 1900, when Freud's groundbreaking book "The Interpretation of Dreams" appeared, the transformation from anatomist to psychologist was complete. His love of anatomy had long ago waned; his commitment to drawing had not.
"I see no necessity to apologize for the imperfections of this or of any similar imagery," Freud wrote of the dream diagrams. "Analogies of this kind are only intended to assist us in our attempt to make the complications of mental functioning intelligible."
He continued, "So far as I know, the experiment has not hitherto been made of using this method of dissection in order to investigate the way in which the mental instrument is put together, and I can see no harm in it.
"We are justified, in my view, in giving free reign to our speculations so long as we retain the coolness of our judgment," Freud wrote, "and do not mistake the scaffolding for the building."