Erasistratus (304 BC-250 BC) is best known for his works on human cadavers and his knowledge of the human body. He is considered the father of physiology.

Erasistratus, considered the father of physiology, was born on the island of Chios in ancient Greece, to a medical family. His father and brother were doctors, and his mother was the sister of a doctor. He studied medicine in Athens and then, around 280 B.C., enrolled in the University of Cos, a center of the medical school of Praxagoras. Erasistratus then moved to Alexandria, where he taught and practiced medicine, continuing the work of Herophilus. In his later years, he retired from medical practice and joined the Alexandrian museum, where he devoted himself to research.

Although Erasistratus wrote extensively in a number of medical fields, none of his works survive. He is best known for his observations based on his numerous dissections of human cadavers (and, it was rumored, his vivisections of criminals, a practice allowed by the Ptolemy rulers). Erasistratus accurately described the structure of the brain, including the cavities and membranes, and made a distinction between its cerebrum and cerebellum (larger and smaller parts). He viewed the brain, not the heart, as the seat of intelligence. By comparing the brains of humans and other animals, Erasistratus rightly concluded that a greater number of brain convolutions resulted in greater intelligence. He also accurately described the structure and function of the gastric (stomach) muscles, and observed the difference between motor and sensory nerves. Erasistratus promoted hygiene, diet, and exercise in medical care.

In his understanding of the heart and blood vessels, Erasistratus came very close to working out the circulation of the blood (not actually discovered until William Harvey in the seventeenth century A.D.), but he made some crucial errors. Erasistratus understood that the heart served as a pump, thereby dilating the arteries, and he found and explained the functioning of the heart valves. He theorized that the arteries and veins both spread from the heart, dividing finally into extremely fine capillaries that were invisible to the eye. However, he believed that the liver formed blood and carried it to the right side of the heart, which pumped it into the lungs and from there to the rest of the body's organs. He also believed that pneumapneuma, a vital spirit, was drawn in through the lungs to the left side of the heart, which then pumped the pneuma through the arteries to the rest of the body. The nerves, according to Erasistratus, carried another form of pneuma, animal spirit.

After Erasistratus, anatomical research through dissection ended, due to the pressure of public opinion. Egyptians believed in the need of an intact body for the afterlife—hence mummification. Real anatomical studies were not resumed until the thirteenth century.

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