The rational soul was something superadded to the bodily mechanism. It was not a part of the body though it was placed in the pineal gland; a part of the brain, which by its sequestered situation and rich blood supply suggested itself as the seat of some important and mysterious function. Its existence was bound up with the integrity of the body, and on the death of the latter the soul departed. But the body did not die because the soul quitted it, it had rather become an unfit habitation for the soul. Without the latter the functions of the healthy body might still proceed automatically, and if the soul influenced action it actuated an existing mechanism, and without that mechanism it could not act, though the mechanism might act without the soul. Thought, understanding, feeling, will, imagination, memory, these were the prerogatives of the soul, and not those of the automatic body. But the movements of the latter, even voluntary movements, depended on a proper disposition of organs, and without this they were wanting or imperfect. Thus to a thoroughgoing mechanism Descartes joined a spiritualistic and immortal entity; and this, to the materialism of the middle of the nineteenth century, was the blemish on his philosophy. Now of all men who have ever lived he is probably the one who has most profoundly influenced modern thought and investigation: to us what he wrote seems strangely modern, and this apparently arbitrary association of spiritualistic and materialistic elements in life seems almost the most modern thing in his writings. Being, he said, was indeed thought, but how could he derive thought from his clockwork body, with its valves and conduits and wires? No more can we derive consciousness from the wave of molecular disturbance passing through afferent nerve and cerebral tracts. We must account for all the energy of this disturbance, from its origin in the receptor organ to its transformation into the wave of chemical reaction in the muscle, and we must regard its transmission as a conservative process. But how does the state of consciousness accompanying the passage through the cortex of this molecular disturbance come into existence? None of the energy of the nerve disturbance has been transformed into consciousness: the latter is not energy nor anything physical. It is something concomitant with the physico-chemical events involved in a nervous process, an “epiphenomenon.” We have to imagine a “parallelism” between the mechanistic body and the mind. But if we admit that consciousness may be an effective agency in our behaviour, what is the difference between modern theories of physico-psychic parallelism and the Cartesian theory of a rational soul in association with an automatic body? Descartes denied the existence in animals other than man of the rational soul; the latter was not necessary. But he, like us, must have been familiar with reflex actions and must have seen that consciousness