Alcmaeon also investigated the functions of the different senses. Because the process of understanding was similar to the rotations of the stars, he thought that the soul, like the stars, was immortal. He speculated that sense organs relayed information to the brain through “passages.” When blood moved to the large blood vessels, the result was sleep, whereas when it became redistributed the result was wakefulness. The specific nature of Alcmaeon’s ideas, and his introduction to medicine of principles unique to that subject, forever changed the practice of medicine and systematic thought about the human body. As Alcmaeon’s successor, Hippokrates (465–370 B.C.E.) was able to build on his thought and establish medicine as a science in its own right.

In founding his own school, Hippocrates (465–370 B.C.E.) formally established medicine as distinct from theurgy (natural magic) and philosophy. He himself had learned medicine from his father and grandfather. According to the Hippocratic School, illness was caused by an imbalance of four humors that were supposed to be equal in the body: black bile, yellow bile, blood, and phlegm. Every disease progressed to a crisis, from which either death or natural recovery would ensue.

Hippocratic medical practice was passive because it was believed that the body would heal itself given rest and immobilization. The therapy was always gentle, and usually only clean water, wine, or balms were used. Being able to predict the course of an illness was considered important.

In his On the Physician, Hippocrates stressed good grooming and a sober demeanor for doctors. It was important to keep records, not only about the patient but also about the patient’s family and circumstances. Mystical causes of illness were dismissed. After Hippocrates’ death, there was little advancement in the principles attributed to him, and some of his professional rules, such as taking case histories and keeping records, fell into disuse.