the great library of that city almost rivaled those of the Museum and Serapeum at Alexandria. It was the competition between these two royal collectors of books that led to the issuing of a decree that no more papyrus was to be exported from Egypt, and thus there was provided the stimulus which led to the discovery or invention of a new and better material on which books might be written--viz., Pergamentum (our parchment), a word coined from the name of the city in which it was invented. _The Development of Different Sects or Schools of Medicine._--Up to the time of the death of Hippocrates medicine maintained the character of a single organized and harmonious body; but, when this great physician had disappeared from the scene and was no longer there to guide the further development of medical science and to keep his followers working shoulder to shoulder with a single spirit and purpose, this hitherto homogeneous body split up into sects or schools, each of which had some favorite doctrine the promulgation of which seemed to each group of adherents to be of great importance. There were at first two such principal groups, viz., the Dogmatics and the Empirics. The former was composed of those who laid great stress upon speculation or theorizing,--that is, upon the use of the reasoning power,--and the latter of men who maintained that actual experience was the only thing of any serious value. The respective leaders of these two groups or sects were Plato and Aristotle. In Raphael’s celebrated painting, “The School of Athens,” these two heroes of philosophy are represented standing side by side--Plato with his right hand elevated and pointing toward heaven, while Aristotle is looking distinctly at the earth. Pictorially, the tendencies of the two schools of philosophy could not have been better represented. Plato’s genius had taken its flight heavenward and was contemplating earthly things from this point of vantage; his method being to ignore system and to look at everything with the eyes of purest love. “Delightfully poetic, but thoroughly unprofitable speculation as to what constitutes scientific truth and perfected morality!” (Friedlaender.) Aristotle, whose father was a physician and a descendant of Aesculapius, was the hero and guiding spirit of those who based their philosophy on experience, on ascertained facts. Like his celebrated pupil, Alexander the Great, who brought whole nations under his sway, he too was a conqueror in every field of human knowledge. His ideas ruled supreme over the minds of men for thousands of years and to-day, although many of them are no longer accepted as valid, Aristotle himself is universally held to have been the greatest thinker and investigator who has ever lived upon this earth. (In chapter XIII. I shall have occasion to say something further regarding the Dogmatics and the Empirics.)