What we call the operations of the mind are functions of the brain, and the materials of consciousness are products of cerebral activity.

Cabanis may have made use of crude and misleading phraseology when he said that the brain secretes thought as the liver secretes bile; but the conception which that much-abused phrase embodies is, nevertheless, far more consistent with fact than the popular notion that the mind is a metaphysical entity seated in the head, but as independent of the brain as a telegraph operator is of his instrument.
It is hardly necessary to point out that the doctrine just laid down is what is commonly called materialism.

In fact, I am not sure that the adjective "crass," which appears to have a special charm for rhetorical sciolists, would not be applied to it.

But it is, nevertheless, true that the doctrine contains nothing inconsistent with the purest idealism.

For, as Hume remarks (as indeed Descartes had observed long before):-- "'Tis not our body we perceive when we regard our limbs and members, but certain impressions which enter by the senses; so that the ascribing a real and corporeal existence to these impressions, or to their objects, is an act of the mind as difficult to explain as that [the external existence of objects] which we examine at present."-- (I.p.