So Galen studied the great apes instead. At the age of 28, he returned home for a while to serve as surgeon to the gladiators. His fame spread, and he went to Rome. In addition to a great deal of fairly decent, concrete advice, he theorized that all life is based on pneuma or spirit. Plants had natural spirit, which causes growth.
Animals have vital spirit, which is responsible for movement.
He believed that cerebrospinal fluid was the animal spirit, and noted that it was to be found in the cerebral vesicles of the brain as well as the spinal cord. He believed it traveled out through the nerves to the muscles, as well as in from the sensory organs. Imbalances among these psychological states, he believed, were one more cause for diseases. It had some influence on people as varied as Alfred Adler, Ivan Pavlov, and Hans Eysenck. It is some time before we again see real progress in medicine and physiology.