With Pythagoras and his disciples numbers played a very important rôle, and the so-called language of numbers was first taught by him. He considered the unit as the essential principle of all things, and designated God by the figure 1 and matter by the figure 2, and then he expressed the universe by 12, as representing the juxtaposition of 1 and 2. As 12 results from multiplying 3 by 4, he conceived the universe as composed of three distinct worlds, each of which was developed in four concentric spheres, and these spheres corresponded to the primitive elements of fire, air, earth, and water. The application of the number 12 to express the universe Pythagoras had received from the Chaldeans and Egyptians--it being the origin of the institution of the zodiac. Although this is digressing, it serves to show what enormous importance the people of that{017} time attached to numbers, especially to the ternary and quarternary periods in the determination of critical days in illness. Pythagoras was the founder of a philosophic system of great grandeur, beauty, and, in one sense, completion, embracing, as it does, and uniting by common bounds God, the universe, time, and eternity; furnishing an explanation of all natural phenomena, which, if not true, was at that time acceptable, and which appears in strong and favorable contrast as against the mythological systems of pagan priests. No wonder that it captivated the imagination and understanding of the thinking young men of that day. Had they continued in the original purity of life and thought in which he indoctrinated them there is no knowing how long the Pythagorean school might have continued. But after it had been dissolved by the storm of persecution, its members were scattered all over Greece and even beyond. Now no longer held by any bonds, many of them revealed the secrets of their doctrine, to which circumstance we owe the little knowledge thereof we now possess. The Pythagoreans apparently first introduced the custom of visiting patients in their own homes, and they went from city to city and house to house in performance of this duty. On this account they were called Periodic or Ambulant physicians, in opposition to the Asclepiadæ, who prescribed only in the temples. Empedocles, of Agrigentum, well known in the history of philosophy, was perhaps the most famous of these physicians. Let the following incident witness his sagacity: Pestilential fevers periodically ravaged his native city. He observed that their appearance coincided with the return of the sirocco, which blows in Sicily on its western side. He therefore advised to close by a wall, as by a dam, the narrow gorge from which this wind blew upon Agrigentum. His advice was followed and his city was made free from the pestilence.