Cajal was born in 1852. As a young man he taught himself to paint and draw but turned to medicine for a career. In his thirties, he learned about a new way to stain tissue developed by the Italian Camillo Golgi: a new silver-based stain that turned some nerve cells completely black while leaving most others entirely untouched, rendering the delicate branches of the nerve processes clearly visible (as seen in the image on the left). "When I saw the very beautiful preparations of the cerebellum... in energetic and varied hues and stained completely... my delight was immense," Cajal wrote.

Cajal used this technique to see and draw nerve cells, some with long, sinuous axons; others fat, with bushy dendrites. His obsessive interest, artistic skill, and evolving understanding of the architecture of the nervous system found expression in beautiful portraits of brain cells and diagrams of nerve fibers. "Realizing that I had discovered a rich field, I proceeded to take advantage of it, dedicating myself to work, no longer merely with earnestness but with fury," he wrote in Recollections. "In proportion as new facts appeared in my preparations, ideas boiled up and jostled each other in my mind."

Although he had only his eyes and his pencils, his drawing in this slide echoes this modern photomicrograph of the same type of cell, which has been injected with a fluorescent dye and imaged with sophisticated optics.