PLATO (B.C. 427-347) in its philosophical aspect studied medicine, not with any idea of practising the art, but merely as a speculative contemplation. The human soul is an emanation from the absolute intelligence. The world is composed of the four elements. Fire consists of pyramidal, earth of cubical, air of octagonal, and water of twenty-sided atoms. Besides these is the æther. Everything in the body has in view the spirit. The heart is the seat of the mind, the lungs cool the heart, the liver serves the lower desires and is useful for divination. The spleen is the abode for the impurities of the blood. The intestines serve to detain the food, so that it might not be necessary to be constantly taking nourishment. The inward pressure of the air accounts for the breathing. The muscles and bones protect the marrow against heat and cold. The marrow consists of triangles, and the brain is the most perfect form of marrow. When the soul is separated from the marrow, death occurs. Sight is caused by the union of the light which flows into and out of the eyes, hearing in the shock of air communicated to the brain and the blood. Taste is due to a solution of sapid atoms by means of small vessels, which vessels conduct the dissolved atoms to the heart and soul. Smell is very transitory, not being founded on any external image. The uterus is a wild beast exciting inordinate desires. Disease is caused by a disturbance of the quantity and quality of the fluids. Inflammations are due to aberrations of the bile. The various fevers are due to the influence of the elements. Mental diseases are the results of bodily maladies and bad education. Diseases fly away before appropriate drugs. Physicians must be the rulers of the sick in order to cure them, but they must not be money-makers.[398]