In Cajal's time, the dominant belief was that the brain and nervous system formed a "reticulum," a web of fibers that conducted nerve signals continuously, through a network of connections that linked it all together. It is certainly a simpler and more plausible idea than the truth that Cajal saw in his microscope: that the brain is stuffed with billions of tiny cells of many different sizes and shapes. Each nerve impulse--each twitch, each thought--travels through the brain by leaping from cell to cell. For that insight, he was awarded the Nobel Prize in 1906, shared with Golgi. Cajal also figured out that nerve cells are polar, meaning that signals enter the cell through the shrubbery of the dendrites at one end and leave through the other end at the whiplike axon.
More than a century later, we have machines that can visualize living structures smaller than the wavelength of light. Yet today's students of neuroscience recognize Cajal's artful and elaborately detailed illustrations of neurons. He is often called one of the fathers of neuroscience but is probably better described as one of its true artists. Thanks to his vision, we all see a new truth.
This is a portrait of Cajal at age 31.