It must be borne in mind, as Dr. Darwin remarked many years ago, that in dealing with memory we have to do not with laws of light, but with laws of life, and that the misleading notion of images or ideas of objects being stored up in the mind has been derived from our experience of the action of light upon the retina. If we would understand the laws of organization in the highest nerve-centres, we shall certainly do well to study organic processes generally; it would be not less absurd to attempt to understand the higher processes without giving attention to the lower, than it would be to attempt to build a house without taking pains to lay its foundations securely. It is a plain matter of observation that other organic elements besides nervous elements perpetuate impressions made upon them, which they may accordingly in a certain sense be said to remember; the virus of smallpox, for example, makes an impression upon all the elements of the body, which they never lose, although it becomes fainter with the lapse of time; in some unknown way it modifies their constitution so that ever afterwards their susceptibilities are changed. The scar which is left after the healing of a wound in a child's finger keeps the same relative proportion to the finger through life, growing as it grows; for the elements of the new tissue not only renew themselves particle by particle, and thus perpetuate it, but they extend it in relation with the growth of the surrounding parts. We need not brave the fire of psychological scorn by calling this retention of impressions _memory_, or care greatly what it is called, so long as due heed is given to the fact; but we may be permitted to perceive in it the same physiological process which, in the cortical [outer] layers of the cerebral [brain's] hemispheres, is the condition of memory, and of habit in thought. Moreover, it may be fairly demanded of the psychologists that they be consistent, and that they no longer use the word memory to denote those mental processes which have been so completely organized that they take place without consciousness; if it be wrong, as they profess, to assume or imply an unconscious memory, it must be still more wrong to assume or imply an unconscious consciousness, as they sometimes do.