With the research summarized in this monumental two volume treatise, Santiago Ramon y Cajal founded modern neuroscience and thus joined Darwin and Pasteur as the leading biologists of the 19th century. Starting around 1887, Cajal refined a neurological staining method developed almost 15 years earlier by the Italian histologist Camillo Golgi, and applied it first to relatively orderly parts of the nervous systems like the cerebellum, spinal cord, and retina. The conclusions he drew about the organization of neural circuits were, however, diametrically opposed to those advocated by Golgi,...