these having been provided by “Nature” with its own specific faculties of attraction and repulsion.

The Three Categories. Any of the operations of the living part may be looked on in three ways, either (a) as a δύναμις, Pg xxx faculty, potentiality; (b) as an ἐνέργεια, which is this δύναμις in operation; or (c) as an ἔργον, the product or effect of the ἐνέργεια.3

Pg xxxi Galen’s
Method. Like his master Hippocrates, Galen attached fundamental importance to clinical observation—to the evidence of the senses as the indispensable groundwork of all medical knowledge. He had also, however, a forte for rapid generalisation from observations, and his logical proclivities disposed him Pg xxxii particularly to deductive reasoning. Examples of an almost Euclidean method of argument may be found in the Natural Faculties (e.g. Book III. chap. i.). While this method undoubtedly gave him much help in his search for truth, it also not unfrequently led him astray. This is evidenced by his attempt, already noted, to apply the biological principle of the φύσις in physics. Characteristic examples of attempts to force facts to fit premises will be found in Book II. chap. ix., where our author demonstrates that yellow bile is “virtually” dry, and also, by a process of exclusion, assigns to the spleen the function of clearing away black bile. Strangest of all is his attempt to prove that the same principle of specific attraction by which the ultimate tissues nourish themselves (and the lodestone attracts iron!) accounts for the reception of food into the stomach, of urine into the kidneys, of bile into the gall-bladder, and of semen into the uterus.

These instances are given, however, without prejudice to the system of generalisation and deduction which, in Galen’s hands, often proved exceedingly fruitful. He is said to have tried “to unite professional and scientific medicine with a philosophic link.” He objected, however, to such extreme attempts at simplification of medical science as that of the Methodists, to whom diseases were isolated entities, without any relationships in time or space (v. p. xv. supra).

He based much of his pathological reasoning upon Pg xxxiii the “humoral theory” of Hippocrates, according to which certain diseases were caused by one or more of the four humours (blood, phlegm, black and yellow bile) being in excess—that is, by various dyscrasiae. Our modern conception of “hormone” action shows certain resemblances with this theory.

Besides observation and reasoning, Galen took his stand on experiment; he was one of the first of experimental physiologists, as is illustrated in the present book by his researches into the function of the kidneys (p. 59 et seq.). He also conducted a long series of experiments into the physiology of the spinal cord, to determine what parts controlled movement and what sensibility.

As a practitioner he modelled his work largely on the broad and simple lines laid down by Hippocrates. He had also at his disposal all the acquisitions of biological science dating from the time of Aristotle five hundred years earlier, and reinforced by the discoveries in anatomy made by the Alexandrian school. To these he added a large series of researches of his own.

Galen never confined himself to what one might call the academic or strictly orthodox sources of information; he roamed the world over for answers to his queries. For example, we find him on his journeys between Pergamos and Rome twice visiting the island of Lemnos in order to procure some of the terra sigillata, a kind of earth which had a reputation for healing the bites of serpents and Pg xxxiv other wounds. At other times he visited the copper-mines of Cyprus in search for copper, and Palestine for the resin called Balm of Gilead.

By inclination and training Galen was the reverse of a “party-man.” In the Natural Faculties (p. 55) he speaks of the bane of sectarian partizanship, “harder to heal than any itch.” He pours scorn upon the ignorant “Erasistrateans” and “Asclepiadeans,” who attempted to hide their own incompetence under the shield of some great man’s name (cf. p. 141).

Of the two chief objects of his censure in the Natural Faculties, Galen deals perhaps less rigorously with Erasistratus than with Asclepiades. Erasistratus did at least recognize the existence of a vital principle in the organism, albeit, with his eye on the structures which the scalpel displayed he tended frequently to forget it. The researches of the anatomical school of Alexandria had been naturally of the greatest service to surgery, but in medicine they sometimes had a tendency to check progress by diverting attention from the whole to the part.

The
Pneuma
or Spirit. Another novel conception frequently occurring in Galen’s writings is that of the Pneuma (i.e. the breath, spiritus). This word is used in two senses, as meaning (1) the inspired air, which was drawn into the left side of the heart and thence carried all over the body by the arteries; this has not a few analogies with oxygen, particularly as its action in the tissues Pg xxxv is attended with the appearance of the so-called “innate heat.” (2) A vital principle, conceived as being made up of matter in the most subtle imaginable state (i.e. air). This vital principle became resolved into three kinds: (a) πνεῦμα φυσικόν or spiritus naturalis, carried by the veins, and presiding over the subconscious vegetative life; this “natural spirit” is therefore practically equivalent to the φῦσις or “nature” itself. (b) The πνεῦμα ζωτικόν or spiritus vitalis; here particularly is a source of error, since the air already alluded to as being carried by the arteries tends to be confused with this principle of “individuality” or relative autonomy in the circulatory (including, perhaps, the vasomotor) system. (c) The πνεῦμα ψυχικόν or spiritus animalis (anima = ψυχή), carried by longitudinal canals in the nerves; this corresponds to the ψυχή.

This view of a “vital principle” as necessarily consisting of matter in a finely divided, fluid, or “etheric” state is not unknown even in our day. Belief in the fundamental importance of the Pneuma formed the basis of the teaching of another vitalist school