The only hypothesis, in short, to which the facts of inward experience give countenance is that _the brain-tracts excited by the event proper, and those excited in its recall, are in part_ DIFFERENT _from each other_. If we could revive the past event without any associates we should exclude the possibility of memory, and simply dream that we were undergoing the experience as if for the first time. Wherever, in fact, the recalled event does appear without a definite setting, it is hard to distinguish it from a mere creation of fancy. But in proportion as its image lingers and recalls associates which gradually become more definite, it grows more and more distinctly into a remembered thing. For example, I enter a friend's room and see on the wall a painting. At first I have the strange, wondering consciousness, 'Surely I have seen that before,' but when or how does not become clear. There only clings to the picture a sort of penumbra of familiarity,--when suddenly I exclaim: "I have it! It is a copy of part of one of the Fra Angelicos in the Florentine Academy--I recollect it there." Only when the image of the Academy arises does the picture become remembered, as well as seen.
=The Conditions of Goodness in Memory.=--The remembered fact being _n_, then, the path N--O is what arouses for _n_ its setting when it _is_ recalled, and makes it other than a mere imagination. The path M--N, on the other hand, gives the cue or occasion of its being recalled at all. _Memory being thus altogether conditioned on brain-paths, its excellence in a given individual will depend partly on the_ NUMBER _and partly on the_ PERSISTENCE _of these paths_.
The persistence or permanence of the paths is a physiological property of the brain-tissue of the individual, whilst their number is altogether due to the facts of his mental experience. Let the quality of permanence in the paths be called the native tenacity, or physiological retentiveness. This tenacity differs enormously from infancy to old age, and from one person to another. Some minds are like wax under a seal--no impression, however disconnected with others, is wiped out. Others, like a jelly, vibrate to every touch, but under usual conditions retain no permanent mark. These latter minds, before they can recollect a fact, must weave it into their permanent stores of knowledge. They have no _desultory_ memory. Those persons, on the contrary who retain names, dates and addresses, anecdotes, gossip, poetry, quotations, and all sorts of miscellaneous facts, without an effort, have desultory memory in a high degree, and certainly owe it to the unusual tenacity of their brain-substance for any path once formed therein. No one probably was ever effective on a voluminous scale without a high degree of this physiological retentiveness. In the practical as in the theoretic life, the man whose acquisitions _stick_ is the man who is always achieving and advancing, whilst his neighbors, spending most of their time in relearning what they once knew but have forgotten, simply hold their own. A Charlemagne, a Luther, a Leibnitz, a Walter Scott, any example, in short, of your quarto or folio editions of mankind, must needs have amazing retentiveness of the purely physiological sort. Men without this retentiveness may excel in the _quality_ of their work at this point or at that, but will never do such mighty sums of it, or be influential contemporaneously on such a scale.