"The brain is matter, like the finger, and by no means fixed and stable matter. It is essentially changing matter, rapidly variable, and forming no identity. A single lobe, a single cell, a single molecule which does not change, does not and could not exist in the whole mass of encephalic matter. A stoppage of motion, of circulation, or of transformation would be a death-warrant. The brain subsists and feels, only on condition of submitting, like all the rest of the body, to the incessant transformations of organic matter which constitute the vital circuit. "So it cannot be that our personality, our identity, lies in a certain grouping of cerebral matter,--our individual me, our _ego_ which acquires and preserves a personal scientific and moral value, increasing with study; our _ego_ which feels itself responsible for its acts performed a month, a year, ten, twenty, fifty years ago, during which time however the molecular grouping has been _changed_ frequently. "Physiologists who affirm that the soul does not exist, are like their ancestors who affirmed that they felt pain in their finger or their foot. They are a little less far from the truth, but they stop on the way when they stop at the brain, and make the human being consist of cerebral impressions. This hypothesis is all the less excusable because these same physiologists know perfectly well that personal sensation is always accompanied by a modification of substance. In other words, the _ego_ of the individual only continues when the identity of its matter ceases to continue. "Our principle of sensibility, then, cannot be a material object; it is put in communication with the universe by cerebral impressions, by the chemical forces disengaged in the encephalon in consequence of material combinations. But it is _different_. "And our organic constitution is perpetually transformed under the direction of a psychic principle. "Some molecule now incorporated in our organism escapes from it by expiration, perspiration, etc., to belong to the atmosphere for a longer or shorter time, then to be incorporated into another organism,--plant, animal, or man. The molecules which actually constitute your body were not all made part of your person yesterday, and none of them were there three months ago. Where were they? Either in the air or in another body. All the molecules now forming your organic tissues, your lungs, your eyes, your brain, your legs, etc., have already served to form other organic tissues. We are all resuscitated dead men, made from the dust of our ancestors. If all the people who have lived up to this time arose from the dead, there would be five of them to every square foot upon the surface of all the continents,--obliged to climb on one another's shoulders in order to stand; but they could not all be completely resuscitated, for many of the molecules have served successively for several bodies.