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:--