ARISTOTLE, the founder of comparative anatomy and the father of the science of natural history, was the son of Nichomachus, physician to Amyntas II., king of Macedonia. He was born at Stageira, B.C. 334. His father was a scientific man of the race of the Asclepiads, and it was the taste for such pursuits and the inherited bent of mind which early inclined the son to the investigation of nature. He went to Athens, where he became the disciple of Plato, and remained in his society for twenty years. In his forty-second year he was summoned by Philip of Macedon to undertake the tuition of Alexander the Great, who was then fifteen years old. Of his philosophical works it is not here necessary to speak; it is his scientific labours, which had so important an influence on medical education, which chiefly concern us. He wrote _Researches about Animals_, _On Sleep and Waking_, _On Longevity and Shortlivedness_, _On Respiration_, _On Parts of Animals_, _On Locomotion of Animals_, _On Generation of Animals_. Aristotle inspired Alexander with a passion for the study of natural history, and his royal pupil gave him abundant means and opportunity to collect materials for a history of animals. The science of comparative anatomy, so important in relation to that of medicine, was thus established. He pointed out the differences which exist between the structure of men and monkeys; described the organs of the elephant, and the stomach of the ruminant animals. The anatomy of birds and the development of their eggs during incubation were accurately described by him; he dissected reptiles, and studied the habits of fishes. He investigated the action of the muscles, regarded the heart as the origin of the blood-vessels, named the _aorta_ and the _ventricles_, described the nerves which he thought originated in the heart, but he confused the nerves with the ligaments and tendons. The heart he considered as the centre of movement and feeling[406] and nourishment, holding that it contains the natural fire, and is the birthplace of the passions and the seat of the soul; the brain he thought was merely a mass of water and earth, and did not recognise it as nervous matter. The diaphragm he considered had no other office than to separate the abdomen from the thorax and protect the seat of the soul (the heart) from the impure influences of the digestive organs. Superfœtation (or the conception of a second embryo during the gestation of the first) he held to be possible, and he first pointed out the _punctum saliens_.