DIOGENES OF APOLLONIA, the eminent natural philosopher, lived at Athens about 460 B.C. He was a pupil of Anaximenes, and wrote a work entitled _On Nature_, in which he treated of physical science generally. Aristotle has preserved for us some of the few fragments which remain. The most important is the description of the origin and distribution of the veins, and is inserted in the third book of Aristotle’s _History of Animals_. Diogenes Laertius gives an account of the philosophical teaching of the philosopher: “He maintained that air was the primal element of all things; that there was an infinite number of worlds, and an infinite void; that air, densified and rarefied, produced the different members of the universe; that nothing was produced from nothing, or was reduced to nothing; that the earth was round, supported in the middle, and had received its shape from the whirling round of the warm vapours, and its concretion and hardening from cold.”[351]
Diogenes recognised no distinction between mind and matter, yet he considered air possessed intellectual energy.
We find in this philosopher many indications that the vascular system was in some degree beginning to be understood.[352] Mr. Lewes and Mr. Grote agree that Diogenes deserves a higher place in the evolution of philosophy than either Hegel or Schwegler.
EMPEDOCLES of Agrigentum, born about 490 B.C., now bears forward the flaming torch of medical science, and in his hands it burns more brightly still. Aristotle mentions him among the Ionian physiologists, and ranks him with the atomistic philosophers and Anaxagoras. These all sought to discover the basis of all changes and to explain them. According to Empedocles: “There are four ultimate kinds of things, four primal divinities, of which are made all structures in the world—fire, air, water, and earth. These four elements are eternally brought into union, and eternally parted from each other, by two divine beings or powers, love and hatred—an attractive and a repulsive force which the ordinary eye can see working amongst men, but which really pervade the whole world. According to the different proportions in which these four indestructible and unchangeable matters are combined with each other is the difference of the organic structure produced; _e.g._, flesh and blood are made of equal parts of all four elements, whereas bones are one-half fire, one-fourth earth, and one-fourth water. It is in the aggregation and segregation of elements thus arising that Empedocles, like the atomists, finds the real process which corresponds to what is popularly termed growth, increase, or decrease. Nothing new comes or can come into being; the only change that can occur is a change in the juxtaposition of element with element.”[353]