In the 'loop-line' along which the memories and ideas of the distant are supposed to lie, the action, so far as it is a physical process, must be interpreted after the type of the action in the lower centres. If regarded here as a reflex process, it must be reflex there as well. The current in both places runs out into the muscles only after it has first run in; but whilst the path by which it runs out is determined in the lower centres by reflections few and fixed amongst the cell-arrangements, in the hemispheres the reflections are many and instable. This, it will be seen, is only a difference of degree and not of kind, and does not change the reflex type. The conception of _all_ action as conforming to this type is the fundamental conception of modern nerve-physiology. So much for our general preliminary conception of the nerve-centres! Let us define it more distinctly before we see how well physiological observation will bear it out in detail. THE EDUCATION OF THE HEMISPHERES. Nerve-currents run in through sense-organs, and whilst provoking reflex acts in the lower centres, they arouse ideas in the hemispheres, which either permit the reflexes in question, check them, or substitute others for them. All ideas being in the last resort reminiscences, the question to answer is: _How can processes become organized in the hemispheres which correspond to reminiscences in the mind?_[6] Nothing is easier than to conceive a _possible_ way in which this might be done, provided four assumptions be granted. These assumptions (which after all are inevitable in any event) are: 1) The same cerebral process which, when aroused from without by a sense-organ, gives the perception of an object, will give an _idea_ of the same object when aroused by other cerebral processes from within. 2) If processes 1, 2, 3, 4 have once been aroused together or in immediate succession, any subsequent arousal of any one of them (whether from without or within) will tend to arouse the others in the original order. [This is the so-called law of association.] 3) Every sensorial excitement propagated to a lower centre tends to spread upwards and arouse an idea. 4) Every idea tends ultimately either to produce a movement or to check one which otherwise would be produced. [Illustration: FIG. 3.]