of the nerve substance is to conduct, to coördinate or to inhibit movements. How then does it come about that 'my perception of the universe' appears to depend upon the internal movements of the cerebral substance, to change when they vary, and to vanish when they cease?
The difficulty of this problem is mainly due to the fact that the grey matter and its modificationsThe brain—an image—cannot create images. are regarded as things which are sufficient to themselves and might be isolated from the rest of the universe. Materialists and dualists are fundamentally agreed on this point. They consider certain molecular movements of the cerebral matter apart: then, some see in our conscious perception a phosphorescence which follows these movements and illuminates their track; for others, our perceptions succeed each other like an unwinding scroll in a consciousness which expresses continuously, in its own way, the molecular vibrations of the cortical substance: in the one case, as in the other, our perception is supposed to translate or to picture the states of our nervous system. But is it possible to conceive the nervous system as living apart from the organism which nourishes it, from the atmosphere in which the organism breathes, from the earth which that atmosphere envelopes, from the sun round which the earth revolves? More generally, does not the fiction of an isolated material object imply a kind of absurdity, since this object borrows its physical properties from
