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.

Galen believed in the doctrine of the four elements, and his speculations led him into a belief in a further subdivision. "Fire is hot and dry; air is hot and moist; for the air is like a vapour; water is cold and moist, and earth is cold and dry." He held that there were three principles in man—spirits, solids, and humours—and eight temperaments ranging between health and disease and compatible with life. He retained a good deal of the teaching of the Pneumatic school, and believed that the pneuma was different from the soul, but the vehicle for the interaction of soul and body. From his theory of the action of the air through the nose on the contents of the ventricles of the brain is explained his use of sternutatories, and his belief in the efficacy of sneezing. Galen's classification of inflammations shows that his pathology was not nearly so accurate as his anatomy and physiology. He described (a) simple inflammation caused by excess of blood alone; (b) inflammation the result of excess of both pneuma and blood; (c) erysipelatous inflammation when yellow bile gains admission, and (d) scirrhous or cancerous when phlegm is present. He did good service by dividing the causes of disease into remote and proximate, the former subdivided into two classes—predisposing and exciting.

IV.—On Diagnosis.

He relied greatly on the doctrine of "critical days," which were thought to be influenced to some extent by the moon. His studies of the pulse were very useful to him in diagnosis. No doubt, he was an expert diagnostician mainly owing to his long, varied, and costly medical education, and his great natural powers of judgment. He asserted that with the help of the Deity he had never been wrong, but even his most ardent admirers would not be wanting in enthusiasm if they amended "never" into "hardly ever."

V.—On Pharmacy, Materia Medica, and Therapeutics.

In these subjects Galen was not as proficient as Dioscorides, whose teaching he adopted with that of other medical authors. In Galen's works there are lengthy lists of compound medicines, several medicines being recommended for the same disease, and never with very marked confidence. He paid high prices for various nostrums, and, sad to relate, placed great faith in amulets, belief in which was general in his time, and nowhere held more strongly than in superstitious Rome. Medicines were classified by him according to their qualities, by which he meant, not their therapeutic effects, but their inherent dryness or moistness, coldness or heat. A medicine might be cold in the first degree, and not in the second degree. Paulus Ægineta followed this strange and foolish doctrine of Galen very closely, as the following extracts from his book on Materia Medica will show:—

"Cistus (rock-rose).—It is an astringent shrub of gently cooling powers. Its leaves and shoots are so desiccative as to agglutinate wounds; but the flowers are of a more drying nature, being about the second degree; and hence, when drunk, they cure dysenteries and all kinds of fluxes."[2]