One of the most indelible images in the history of cinema evokes the sectioning of an eye in a Cajal laboratory.

Excerpt from The Brain in Search of Itself. Santiago Ramón y Cajal and the History of the Neuron (Ladera Norte Publishing House), a new book by American writer Benjamin Ehrlich , in which he portrays the greatest Spanish scientist of all time, winner of the Nobel Prize in Medicine in 1906 after demonstrating that the nervous system is organized into individual cells: neurons.

Having retired from his social gathering, Cajal looked for a cooler, more solitary café where, after lunch, he could sit for an hour or two undisturbed and read the newspaper, hoping to forestall migraines. He found the Café del Prado , which was practically empty during the day. Without taking off his old, threadbare, faded, caramel-colored overcoat, he would sit in a corner facing the window, facing the sun, stirring his coffee with a spoon, his bald head bowed, muttering to himself and taking notes. “He is bent over the whole thing under the weight of many thoughts,” one visitor to the café would observe. “This little old man, trembling and nervous, who seems dazed,” wrote another regular, “this one is the honor, glory, and pride of Spain!” Frequently, said one old waiter, he would forget his hat or his cane, but never leave a good tip.

At a table across the café sat a boisterous group of young artists, including Luis Buñuel , who was 22 at the time, and Salvador Dalí , 18. They called themselves ultraists, the most radical of the avant-garde.

Buñuel's first ambition was to become a piano composer, but his father, a descendant of a family of Aragonese businessmen, steered him toward a more practical profession. When Buñuel arrived at the Residencia de Estudiantes in 1917, he began studying Agronomy, but at the Residencia, as he himself said, "you could prepare for any subject [...]. You could stay as long as you wanted and change subjects during the course." Driven by his childhood fascination with insects, Buñuel changed his major and began studying Natural Sciences.

Behind the Residencia was the Natural History Museum, where Cajal had installed four of the Junta's laboratories. Buñuel joined the laboratory of Ignacio Bolívar , a celebrated entomologist in his seventies who had been one of the researchers who had encouraged Cajal to study microscopy when he had visited Madrid decades earlier.

Two years after Buñuel, Federico García Lorca , a dark-skinned and devilishly charming young man from a wealthy Andalusian family, arrived at the Residencia. “Our friendship, which was deep, dates back to our first meeting,” Buñuel recalled. Lorca's first love was also the piano, and he was known for singing while accompanying himself on it in spontaneous public recitals. He would simulate his own death with all sorts of intense and gruesome details, lying in bed and convulsing, and then, when he saw his friends were frightened, bursting into laughter. Lorca and Buñuel would go for walks together in the Residencia's garden, in the shade of the poplars; they would sit on the grass, and Federico would recite his poetry to Buñuel.

Three years after Lorca came Salvador Dalí, a young man from a small Catalan town with long hair and sideburns who wore shorts and stockings. His father was very strict and authoritarian, and it was his mother who encouraged his artistic talent. He was expelled from the Academy of Fine Arts for refusing to be examined by a group of professors, as he insisted he knew more than they did. When he arrived at the Residencia, there were no Cubists in Madrid; he was inspired by a French art magazine. Two of his early Cubist paintings appear to depict Lorca giving a poetry recital. In the annual production of Don Juan Tenorio , Dalí acted, Lorca handled the staging or directed, and Buñuel, a famous party animal and womanizer, played the lead role, which he seemed born to play.

Hundreds of years after the Golden Age, Madrid was still a place where literary or artistic disputes could come to blows. In 1922, the same year Cajal retired, one writer slapped another in the street, which led to a duel. The Ultraists organized a banquet to honor one of the two writers, because they considered the other to be a pretentious fraud. They sent the invitation to many of Madrid's intellectuals, and all responded, except Cajal. Since Buñuel had worked in one of the laboratories of the solitary scholar who sat across the café, he was the one chosen by the Ultraists to get his signature.

With thick black eyebrows, full, defined lips, a wide, misshapen nose, and squinting, bulging eyes, Buñuel's face was vaguely Cubist. A self-described "coarse Aragonese," Buñuel had grown up in the village of Calanda, located in southern Aragon, the same region where Cajal had grown up. Both were macho men. Competitive and conceited. Buñuel once said that if he could take just one book to a desert island, it would be Fabre's The Life of Insects , also one of Cajal's favorites. Cajal probably didn't notice him at first. "Don Santiago," said Buñuel, addressing him with the utmost respect. "I am Buñuel. I don't know if you remember me. I have prepared many fly corneas for you . I was working with Bolívar." Then he asked Cajal if he would sign the summons. The latter looked up. "Friend Buñuel, I will not sign." The "pretentious fraud" whom the Ultraists hated was a journalist who had written that, although he had interviewed millionaires, war heroes, and even members of the royal family, he had never felt in the presence of true greatness until he met him. When Buñuel recounted the anecdote in his memoirs sixty years later, almost at the end of his life, he not only did not mock Cajal's behavior, but he excused it: he had done what anyone in his situation would have done.

Cajal, for his part, despised modern painting. He called avant-garde art a “multiform and contradictory jumble of schools,” baptized with “pompous names” like Cubism and Expressionism, to which belonged paintings that seemed to him to have been done by lunatics or children. Picasso's works, in his opinion, were nothing more than “deliberate idiocies.” “In art, as in science,” he wrote in a notebook with observations on works in the Prado Museum, “there are norms and canons that represent the progress of many centuries.” He described the elongated heads in El Greco portraits—whose quality had recently been vindicated by the avant-garde movements—as “microencephalic,” a medical term for brains that have not developed normally. He believed that the ideal was nature itself, which artists should strive to capture clearly so that their canvases depicted the external world as faithfully as possible. Surrealism violated the sacred, objective, logical reality. He had intended to write a book of art criticism entitled The Pathology of Art , but another scholar, who had the same idea, beat him to it.

Although he rejected the style, Cajal ultimately served as an inspiration to those who would become the most important Spanish artists since the Golden Age. Experts have pointed out that the drawings Dalí and Lorca made during their stay at the Residencia bore a certain resemblance to his own. His legacy was omnipresent there.

In 1929, Buñuel and Dalí wrote the iconic short film Un Chien Andalou together. The film opens with Buñuel smoking a cigarette and sharpening a razor blade. He then steps out onto a terrace and looks up as thin clouds drift across the night sky toward a white full moon. The next scene is a close-up of a woman's face; a man's hand holds her eyelids open and begins to cut her eye with a razor blade. One of the most indelible images in film history evokes the sectioning of a fly's cornea in Cajal's laboratory.