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VITALISM : A BRIEF HISTORICAL AND CRITICAL REVIEW. 223 the heart from a -jrvevfjM ifrvxtKov in the brain, and, refuting the internal perfecting principle of Aristotle, denied the current Stoical belief in the rule of a wisdom of Providence over the body. The school of the Pneumatics proper finds its ablest ex- ponents in the persons of Athenseus, Aretseus and Archigenes. Athenaeus of Attaleia (fl. 50 A.D.), adding to the two pneu- mata of Erasistratus a third, the -n-vev^a <}>V<TIKOV, maintained that disease resulted from certain changes in the pneumata. It is here unnecessary to refer to the clinical observations and teaching of Aretasus (fl. 150 A.D.), and Archigenes, close followers of Hippocrates. The pneumatic doctrine received its fullest development at the hands of Galen, beneath the shadow of whose authority it was destined to flourish for many centuries. Claudius Galen (131 to about 200 A.D.) was the first in the history of Natural Science in whom an honest desire is found expressed to collect all phenomena into a mutually dependent system before the construction therefrom of philosophical speculation be attempted. Grasping the importance of anatomical research as a basis for the comprehension of physiological function, Galen undertook the dissection and (we are told) the vivisection of various animals. The ex- tensive view of life thus acquired led to his celebrated elaboration of the pneumatic doctrine. Besides the -rrvev^a (oTiic6it and the 7rvevfj.a ^V^IKOV of Erasistratus, Galen, like Athenaeus, added a irvevpa (frvo-ixov which, resident in the liver, he endowed with the power (Swapis) of nutrition, growth, secretion, reproduction, etc. Galen's conception of the circulation is worthy of mention. To his mind the venous blood, originating in the liver, travelled to the right side of the heart where a dual separation took place, the living portion proceeding to the left side of the heart, the dead portion being carried to the lungs, there to undergo a process of "refreshment" under the influence of the external pneuma. With the prophetic instinct of true genius, Galen suspected that the life-giving pneuma would some day be isolated from the air which held it. To Hippocrates all theorists have appealed, whether solidists, humorists, dyna- mists, animists or vitalists. All schools too have quoted Aristotle whose metaphysical or physiological studies were in turn adduced, according as a subjective or objective method of study was being advocated. But with the advent of Galen comes for the first time a theory that leaves no doubt as to its nature. The mode in which Aristotle's teachings and discoveries