Aristotle's Psychology: On the Soul and Parva Naturalia

punctum saliens leaping point of later writers) which palpitates and whose movements are those of an organism endowed with life.

The heart is at once the physiological and psychical centre of man. In as much as Aristotle identifies life with soul, it is a matter of consistency for him to place the seat of the soul in the vital centre. He rejects the doctrine of Plato and Diogenes of Apollonia, who regarded the brain as the organ of mind. To Aristotle the brain is merely a regulator for the temperature of the heart; the brain is bloodless and cool, and the blood and warm vapours from the heart rising to this are lowered in temperature. By this physiological device, conjoined with the service of respiration, Aristotle supposes that the system is maintained in a heat-equilibrium.

The material element in which the soul is immediately incorporated is heat or fire, but the soul is not identical with this, as Democritus thought. Nor is the vital heat ordinary fire, but some subtle principle analogous perhaps, as Ogle says,1 to that imponderable and hypothetical matter of the physicists known as Ether. In accordance with his theory, Aristotle was naturally forced to attribute vital heat to plants and the cold-blooded animals, but his grounds for this position are not to be found in any of the extant works. He had, of course, no knowledge of the chemical elements of oxygen and carbon. The vital caloric of the body is kept up by food which serves as fuel. This heat which, according to Descartes, is produced by fermentation or, according to Haller, by friction between

1 Aristotle, On Youth and Old Age, trans. by Ogle, Introd. p. 9.