He regarded the structure of various parts, such as the hand and the membranes of the brain, as absolute perfection, although his idea of the human hand was derived from a study of the ape's, and he had no knowledge of the arachnoid membrane of the brain, but it would be unfair to criticize his conclusions because of his failure to recognize a few comparatively unimportant details. He discovered the function of the motor nerves by cutting them experimentally, and so producing paralysis of the muscles; the platysma, interossei, and popliteus muscles were first described by him. He was the greatest authority on the pulse, and he recognized that it consisted of a diastole (expansion) and a systole (contraction) with an interval after the diastole, and another after the systole. Aristotle thought that arteries contained air, but Galen taught that they contained blood, for, when an artery was wounded, blood gushed out. He was not far from the discovery of the circulation. He described the heart as having the appearance of a muscle, and considered it the source of natural heat, and the seat of violent passions. He knew well the anatomy of the human skeleton, and advised students to go to Alexandria where they might see and handle and properly study the bones. He recognized that inspiration is associated with enlargement of the chest, and imagined that air passed inside the skull through the cribriform plate of the ethmoid bone, and passed out by the same channel, carrying off humours from the brain into the nose. But some of this air remained and combined with the vital spirits in the anterior ventricles of the brain, and finally exuded from the fourth ventricle, the residence of the soul. Aristotle had taught that the heart was the seat of the soul, and the brain relatively unimportant. II.--WORKS ON DIETETICS AND HYGIENE. Galen was a strong advocate of exercises and gymnastics, and eulogizes hunting specially. He recommends cold baths for people in the prime of life. As old age is "cold and dry," this is to be treated with hot baths and the drinking of wine. He thought that wine was particularly suitable for the aged, and that old people required three meals a day, others two meals. He had a very high opinion of pork as an article of diet, and said that the strength of athletes could not be maintained without this form of food. III.--ON PATHOLOGY.