This book, together with the next two volumes to follow, offers the scientific community the works and thoughts of Santiago Ram?n y Cajal. The text is a faithful rendition of the original Spanish version, with additional facts taken from the French translation. Both of these are currently quoted an average of 200 times a year in the scientific literature. This collection will represent the definitive Cajal for scientists and scholars interested in the original thoughts of probably the most prominent neuroscientist of all time.An annotated and edited translation of the original Spanish text with the additions of the French version by Pedro Pasik and Tauba PasikMost scientists agree that the 21st century will be the Century of Biology . The revolution that started a few decades ago with the extraordinary develop? ment of molecular biology, has provided the basis for the understanding of the mechanisms that govern life through the regulation of cell function and cell-to? cell interactions. Neuroscience will surely be one of the biological disciplines that will profit the most from this revolution. Neuroscience comprises the study of the brain, and the more difficult relationship of brain and behavior. It is indeed a very broad field of investigation that, from molecular biology and genetics, passing through systems physiology, functional mapping of the brain, and even human behavior, has as the ultimate goal the understanding of how the brain works. The importance of this aim is immense, since it is the only scientific approach to understanding ourselves. Today, owing to the great progress made in neuroscientific research, there is a real hope that highly complex processes such as sensory perception, ICTlg? term memory, learning and others will soon be comprehended in their entirety.I General concept of the nervous system.Structural plan of the neural centers in the animal series.- II Review of research methods and resulting discoveries.- III Components of the nervlC