Leonardo da Vinci as physiologist.

It is of course in the art (or as Leonardo would have called it, the ' science') of representing the parts of the human body that Leonardo stands pre-eminent, but beyond this task of anatomical illustration Leonardo always searched into the problems of function which lay inherent in the accurate representation of each ' instrument of the body.' At the outset he realized that no intelligent discussion of the function of an organ can be under-taken without a clear knowledge of its structure. For many years Leonardo took delight in representing human organs with all his realistic artistry; later on we find his figures becoming less artistic as they become instruments designed to illustrate conceptions of function rather than naturalistic representations, a change that reflects his increasing interest in physiology. In a passage that reads as if it were written as a preface, written with a view to publication, Leonardo writes: ' Therefore there shall be revealed to you in iS complete figures the cosmo-graphy of the minor mondo (the microcosm or lesser world) in the same order as was used by Ptolemy before me in his cosmography. And therefore I shall divide the members as he divided the whole into provinces, and then I shall define the functions of the parts from all aspects, placing before your eyes the knowledge of the whole figure and healthy capacity of man in so far as it has local movement by means of its parts.' It will be noted here that ' local movement' was what interested Leonardo. 'Movement is the cause of all life,' he says. Physiology for Leonardo, then, is mainly the study of all movement in the body, which he appreciates is governed by the senses and the soul. Having represented to his own satisfaction the 'instruments' of the, body as he repeatedly calls human organs, he proceeds to analyze their action. In this analysis he utilizes three lines of attack: i. His own mechanical principles. 2. The Galenic principles of physiology. 3. The analogy between the macrocosm and the microcosm as mentioned in the above quotation. All his physiological views will be found to contain a blend of these three components. The macrocosm-microcosm analogy is repeatedly cited in Leonardo's notes. In one example he gives his reasons for accepting its importance -' Man has been called by the ancients a lesser world, and indeed the term is rightly …