How it began
In 1888 the Spanish histologist Santiago Ramón y Cajal proposed that the nervous system was not one large continuous network of fibers. Studying stained nervous tissue under the microscope, he found that nerve cells had gaps between them and communicated by contact. He recorded what he saw in detailed drawings of neural architecture, which are still reproduced and are regarded as works of art as well as scientific records.
Before it existed
Nineteenth-century scientists generally held the reticular theory: that all the components of the nervous system formed a single continuous, maze-like network of fibers. The tools for testing this were limited, because nervous tissue is dense and ordinary stains colored everything at once. In 1873 the Italian Camillo Golgi published the black reaction, which used potassium dichromate and silver nitrate to stain a small number of cells completely.
How it works
Cajal learned of Golgi's stain and modified and popularized it. He chose to apply it to embryonic and young tissue, where the cells are fewer and less tangled, which made individual cells easier to follow from end to end. What he saw supported the idea that each neuron is a distinct unit and that neurons pass signals to one another at specialized points of contact, the junctions now called synapses, instead of being fused into one web.
Who pushed back
Golgi himself never accepted the conclusion. He and Cajal shared the Nobel Prize in Physiology or Medicine in 1906, yet they opposed each other in their beliefs: Golgi held to the reticular theory while Cajal presented mounting evidence against it. The question was not finally settled in their lifetimes, and the two men used their shared prize to argue for opposite conclusions.
What lasted
In the twentieth century electron microscopy confirmed that nerve cells are separate, and the neuron doctrine prevailed. The idea that the neuron is the basic unit of the nervous system became the foundation of neuroscience, and Cajal is described as the father of the modern field. He went on to extend the doctrine with work on the growth, plasticity, degeneration and regeneration of nerve cells.
