keynote of the teaching of both Hippocrates and Galen; this is shown in the volume before us, which deals with “the natural faculties”—that is with the faculties of this same “Nature” or vital principle referred to in the quotation.

“The
Natural
Faculties.” If Galen be looked on as a crystallisation of Greek medicine, then this book may be looked on as a crystallisation of Galen. Within its comparatively short compass we meet with instances illustrating perhaps most of the sides of this many-sided writer. The “Natural Faculties” therefore forms an excellent prelude to the study of his larger and more specialised works. Pg xxvi

Galen’s
“Physiology.” What, now, is this “Nature” or biological principle upon which Galen, like Hippocrates, bases the whole of his medical teaching, and which, we may add, is constantly overlooked—if indeed ever properly apprehended—by many physiologists of the present day? By using this term Galen meant simply that, when we deal with a living thing, we are dealing primarily with a unity, which, quâ living, is not further divisible; all its parts can only be understood and dealt with as being in relation to this principle of unity. Galen was thus led to criticise with considerable severity many of the medical and surgical specialists of his time, who acted on the assumption (implicit if not explicit) that the whole was merely the sum of its parts, and that if, in an ailing organism, these parts were treated each in and for itself, the health of the whole organism could in this way be eventually restored.

Galen expressed this idea of the unity of the organism by saying that it was governed by a Physis or Nature (ἡ φύσις ἥπερ διοικεῖ τὸ ζῷον), with whose “faculties” or powers it was the province of φυσιολογία (physiology, Nature-lore) to deal. It was because Hippocrates had a clear sense of this principle that Galen called him master. “Greatest,” say the Moslems, “is Allah, and Mohammed is his prophet.” “Greatest,” said Galen, “is the Physis, and Hippocrates is its prophet.” Never did Mohammed more zealously maintain the unity of the Godhead than Hippocrates and Galen the unity of the organism. Pg xxvii

Galen’s
Physics. But we shall not have read far before we discover that the term Physiology, as used by Galen, stands not merely for what we understand by it nowadays, but also for a large part of Physics as well. This is one of the chief sources of confusion in his writings. Having grasped, for example, the uniqueness of the process of specific selection (ὁλκὴ τοῦ οἰκείου), by which the tissues nourish themselves, he proceeds to apply this principle in explanation of entirely different classes of phenomena; thus he mixes it up with the physical phenomenon of the attraction of the lodestone for iron, of dry grain for moisture, etc. It is noteworthy, however, in these latter instances, that he does not venture to follow out his comparison to its logical conclusion; he certainly stops short of hinting that the lodestone (like a living organ or tissue) assimilates the metal which it has attracted!

Setting aside, however, these occasional half-hearted attempts to apply his principle of a φύσις in regions where it has no natural standing, we shall find that in the field of biology Galen moves with an assurance bred of first-hand experience.

The
Mechanical
Physicists. Against his attempt to “biologize” physics may be set the converse attempt of the mechanical Atomist school. Thus in Asclepiades he found a doughty defender of the view that physiology was “merely” physics. Galen’s ire being roused, he is not content with driving the enemy out of the biological camp, but must needs attempt also to Pg xxviii dislodge him from that of physics, in which he has every right to be.

The Anatomists. In defence of the universal validity of his principle, Galen also tends to excessive disparagement of morphological factors; witness his objection to the view of the anatomist Erasistratus that the calibre of vessels played a part in determining the secretion of fluids (p. 123), that digestion was caused by the mechanical action of the stomach walls (p. 243), and dropsy by induration of the liver (p. 171).

Characteristics
of the
Living
Organism. While combating the atomic explanation of physical processes, Galen of course realised that there were many of these which could only be explained according to what we should now call “mechanical laws.” For example, non-living things could be subjected to φορά (passive motion), they answered to the laws of gravity (ταῖς τῶν ὑλῶν οἰακιζόμενα ῥοπαῖς, p. 126). Furthermore, Galen did not fail to see that living things also were not entirely exempted from the operation of these laws; they too may be at least partly subject to gravity (loc. cit.); a hollow organ exerts, by virtue of its cavity, an attraction similar to that of dilating bellows, as well as, by virtue of the living tissue of its walls, a specifically “vital” or selective kind of attraction (p. 325).

As a type of characteristically vital action we may take nutrition, in which occurs a phenomenon Pg xxix which Galen calls active motion (δραστικὴ κίνησις) or, more technically, alteration (ἀλλοίωσις). This active type of motion cannot be adequately stated in terms of the passive movements (groupings and re-groupings) of its constituent parts according to certain empirical “laws.” Alteration involves self-movement, a self-determination of the organism or organic part. Galen does not attempt to explain this fundamental characteristic of alteration any further; he contents himself with referring his opponents to Aristotle’s work on the “Complete Alteration of Substance” (p. 9).

The most important characteristic of the Physis or Nature is its τέχνη—its artistic creativeness. In other words, the living organism is a creative artist. This feature may be observed typically in its primary functions of growth and nutrition; these are dependent on the characteristic faculties or powers, by virtue of which each part draws to itself what is proper or appropriate to it (το οἰκεῖον) and rejects what is foreign (το ἀλλότριον), thereafter appropriating or assimilating the attracted material; this assimilation is an example of the alteration (or qualitative change) already alluded to; thus the food eaten is “altered” into the various tissues of the body, each of