In any case, the foregoing considerations cannot fail to show how misleading it is to look upon perceptions as mere pictures of nature, and upon the mind as a vast canvas on which they are cunningly painted; the real process is one of organization, and it is rightly conceivable only by the aid of ideas derived from the observation of organic development--namely, the fundamental ideas of Assimilation of the like and Differentiation of the unlike. Nowhere is it more necessary than in the study of memory to apprehend clearly that what we call mind is the function of a mental organization; for thereby we get rid at once of many empty discussions which have been carried on without definite result; as, for example, whether memory is a knowledge of the past, or a knowledge of the present with a belief of the past, and the like. Moreover, this conception of a mental organization is indispensable to the explanation of the manifold varieties of partial or general loss of memory which are produced by injury, disease and decay of brain; for memory is good or bad according to bodily states, is impaired in various ways by disease, decays with the decay of structure in old age, and is extinguished with the extinction of life in the brain. From of old two kinds of memory have been distinguished, according as the object remembered occurs to the mind spontaneously, or is voluntarily sought for; the former being known as _memory_ proper, the latter as _recollection_. It is certain that we do recognize this difference, which common language attests, between that which is revived without any effort, and that which we endeavour to recover by an effort; and that men differ much, by virtue of natural capacities, both in memory and in power of recollection. No doubt much of the difference in both cases is due to the degree of attention which is given to the subject when it is first presented to the mind, but this will not account satisfactorily for all the difference which is observed; some persons being able to repeat with great ease a row of figures, a number of dates, or several lines of poetry, after reading them over once, while others fail to do so with equal success after reading them over many times. Extraordinary instances have been recorded of this exactness of memory for details reaching back to the earliest periods of life. I have seen an imbecile in the Earlswood Asylum for idiots who can repeat accurately a page or more of any book which he has read years before, even though it was a book which he did not understand in the least; and I once saw an epileptic youth, morally imbecile, who would, shutting his eyes, repeat a leading article in a newspaper word for word, after reading it once. This kind of memory, in which the person seems to read a photographic copy of former impressions with his mind's eye, is not indeed commonly associated with great intellectual power; for what reason I know not, unless it be that the mind to which it belongs is