Alcmaeon of Croton in Wikipedia
Alcmaeon (Gr. Ἀλκμαίων, Alkmaiōn, gen.: Ἀλκμαίωνος; 5th century BC) of Croton (in Magna Græcia) was one of the most eminent natural philosophers and medical theorists of antiquity. His father's name was Peirithus (Peirithos). He is said by some to have been a pupil of Pythagoras, and he may have been born around 510 BC. Although he wrote mostly on medical topics there is some suggestion that he was not a physician but a philosopher of science; he also indulged in astrology and meteorology. Nothing more is known of the events of his life.
He was considered by many an early pioneer and advocate of anatomical dissection and was said to be the first to identify Eustachian tubes. His celebrated discoveries in the field of dissection were noted in antiquity, but whether his knowledge in this branch of science was derived from the dissection of animals or of human bodies is still a disputed question. Calcidius, on whose authority the fact rests, merely says "qui primus exsectionem aggredi est ausus," and the word exsectio would apply equally well in either case; some modern scholars doubt Calcidius' word entirely.
He also was the first to dwell on the internal causes of illnesses. It was he who first suggested that health was a state of equilibrium between opposing humors and that illnesses were because of problems in environment, nutrition and lifestyle. He is said also to have been the first person who wrote on natural philosophy (φυσικὸν λόγον), and to have invented fables. He also wrote several other medical and philosophical works, of which nothing but the titles and a few fragments have been preserved by Stobaeus, Plutarch, and Galen. His Concerning Nature might be the earliest example of Greek medical literature.
Alcmaeon of Croton expiremented with live animals by cutting the nerve behind the eye to study vision. He also contributed to the study of medicine by establishing the connection between the brain and the sense organs, and outlined the paths of the optic nerves as well as stating that the brain is the organ of the mind. However, his theories were not without mistakes. He said that sleep occurs when blood vessels in the brain are filled and that waking is caused by the emptying of these vessels. He also stated that the eye contains both fire and water.
Although Alcmaeon is often called a pupil of Pythagoras, there is great reason to doubt whether he was a Pythagorean at all; his name seems to have crept into lists of Pythagoreans given us by later writers. Aristotle mentions him as nearly contemporary with Pythagoras, but distinguishes between the stoicheia (στοιχεῖα) of opposites, under which the Pythagoreans included all things; and the double principle of Alcmaeon, according to Aristotle, less extended, although he does not explain the precise difference. Other doctrines of Alcmaeon have been preserved to us. He said that the human soul was immortal and partook of the divine nature, because like the heavenly bodies it contained in itself a principle of motion. The eclipse of the moon, which was also eternal, he supposed to arise from its shape, which he said was like a boat. All his doctrines which have come down to us relate to physics or medicine; and seem to have arisen partly out of the speculations of the Ionian School, with which rather than the Pythagorean, Aristotle appears to connect Alcmaeon, partly from the traditional lore of the earliest medical science.