receives a commission from his friend, and, that he may not forget it, ties a knot in his handkerchief. How is this fact to be explained? First of all, the idea of the commission is associated with the making of the knot. Next, the handkerchief is a thing which it is known beforehand will be frequently seen, and of course at no great distance of time from the occasion on which the memory is desired. The handkerchief being seen, the knot is seen, and this sensation recalls the idea of the commission, between which and itself the association had been purposely formed." In short, we make search in our memory for a forgotten idea, just as we rummage our house for a lost object. In both cases we visit what seems to us the probable _neighborhood_ of that which we miss. We turn over the things under which, or within which, or alongside of which, it may possibly be; and if it lies near them, it soon comes to view. But these matters, in the case of a mental object sought, are nothing but its _associates_. The machinery of recall is thus the same as the machinery of association, and the machinery of association, as we know, is nothing but the elementary law of habit in the nerve-centres. =It also explains retention.= And this same law of habit is the machinery of retention also. Retention means _liability_ to recall, and it means nothing more than such liability. The only proof of there being retention is that recall actually takes place. The retention of an experience is, in short, but another name for the _possibility_ of thinking it again, or the _tendency_ to think it again, with its past surroundings. Whatever accidental cue may turn this tendency into an actuality, the permanent _ground_ of the tendency itself lies in the organized neural paths by which the cue calls up the memorable experience, the past associates, the sense that the self was there, the belief that it all really happened, etc., as previously described. When the recollection is of the 'ready' sort, the resuscitation takes place the instant the cue arises; when it is slow, resuscitation comes after delay. But be the recall prompt or slow, the condition which makes it possible at all (or, in other words, the 'retention' of the experience) is neither more nor less than the brain-paths which _associate_ the experience with the occasion and cue of the recall. _When slumbering, these paths are the condition of retention; when active, they are the condition of recall._ [Illustration: FIG. 62.]