1. The Primitive Period, or that of Instinct, beginning with myth, and ending with the destruction of Troy 1184 years before Christ.
2. The Sacred, or Mystic, Period, ending with the dispersion of the Pythagorean Society, 500 years before Christ.
3. The Philosophic Period, terminating with the foundation of the Alexandrian library, 320 years before Christ.
4. The Anatomic Period, ending with the death of Galen, about A.D. 200.
THE SECOND AGE, OR THAT OF TRANSITION, is divided into a fifth, or Greek Period, ending at the burning of the Alexandrian library, A.D. 640, and a sixth, Arabic Period, ending with the revival of letters, A.D. 1400.
THE THIRD AGE, OR THAT OF RENOVATION, includes the seventh, or Erudite Period, comprising the fifteenth and sixteenth centuries, and eighth, or Reform Period, comprising the seventeenth, eighteenth, and nineteenth centuries.
Examining this table for a moment, it will be seen that so far we have dealt with the Primitive Period and the Sacred, or Mystic, Period. Before passing on to the Philosophic Period let us for a moment follow Renouard, who likens the three schools of medical belief in the earlier part of the Primary Age, or the Age of Foundation, to the three schools of cosmogony, which obtained among the Greeks. The first of these was headed by Pythagoras, who regarded the universe as inhabited by acknowledged sentient principles which governed all substances in a determined way for preconceived purposes. Animals, plants, and even minerals were supposed to possess vivifying spirits, and above them all was a supreme principle. To this school corresponded the so-called Dogmatic School of medicine, attributed to Hippocrates, which was the precursor of modern vitalism, and regarded diseases as indivisible units from beginning to termination; in other words, they consisted of a regular programme of characteristic systems, successive periods, and of long course, either for the better or worse; that was one of the characteristic dogmas of the Hippocratic teaching. The Second System of cosmogony was that founded by Leucippus and Democritus, who explained all natural phenomena without recourse to the intervention of intelligent principles. All things for them existed as the necessary result of the eternal laws of matter. They denied preconceived purposes and ridiculed final causes. To this system corresponded that in medicine which has been termed Methodism (medically and literally speaking) and which recognized as its founders Æsculapius and Themison. The believers in this doctrine attempted to apply the atomic theory of Democritus and Epicurus to the theory and practice of medicine. Atoms of various size were supposed to pass and repass without cessation through cavities or pores in the human body. So long as the atoms and pores maintained a normal relationship of size and proportion health was maintained, but it was deranged so soon as the exactness of these relations was destroyed or interfered with. The Dogmatists considered vital reaction as a primary phenomenon, while with the Methodists it was secondary. The Third System of cosmogony, founded by Parmenides and Pyrrho, believed in the natural improvement of bodies in their endless reproduction and change, and concluded that wisdom consisted in remaining in doubt; in other words, they were the agnostics of that day. "What is the use," said they, "of fatiguing the mind in endeavoring to comprehend what is beyond its capability." Later they were known as Skeptics and Zetetics, to indicate that they were always in search of truth without flattering them selves that they had found it. To them corresponded a third class of physicians, with Philinus and Serapis at their head, who deemed that proximate causes and primitive phenomena of disease were inaccessible to observation; that all that is affirmed on these subjects is purely hypothetical, and hence unworthy of consideration in choosing treatment. For them objective symptoms—or, as we would say, signs—constituted the natural history of disease, they thus believing that their remedies could only be suggested by experience, since nothing else could reveal itself to them. They therefore took the name of Empirics.
Finally a fourth class of physicians arose who would not adopt any one of these systems exclusively, but chose from each what seemed to them most reasonable and satisfactory. They called themselves Eclectics, wishing thereby to imply that they made rational choice of what seemed best. The idea conveyed in the term "eclecticism" has been fairly criticised for this reason: eclecticism is in reality neither a system nor a theory; it is individual pretension elevated to the dignity of dogma. The true eclectic recognizes no other rule than his particular taste, reason, or fancy, and two or more eclectics have little or nothing in common. If that were true two thousand years ago, it is not much less so to-day. The eclectic carefully avoids the discussion of principles, and has neither taste nor capacity for abstract reasoning, although he may be a good practitioner; not that he has no ideas, but that his ideas form no working system. With him medical tact—i.e., cultivated instinct—replaces principle.
The eclectic of our day, however, is only an empiric in disguise,—that is, a man whose opinions are based on comparison of observed facts, but whose theoretical ideas do not go beyond phenomena.
In older days philosophy embraced the whole of human knowledge, and the philosopher was not permitted to be unacquainted with any of its branches. Now physics, metaphysics, natural history, etc., are arranged into separate sciences, and the sum-total of knowledge is too great to be compassed by any one man.