Some quite different explanation must therefore be sought for the varying degrees in which pleasure accompanies normal activities. Can we find this in a suggestion of Mr. Spencer’s, developed by Mr. Grant Allen,[146] that the pleasurableness of normal organic activities depends on their _intermittence_, and that “the amount of pleasure is probably ... in the inverse ratio of the natural frequency of excitation” of the nerve-fibres involved? This theory certainly finds some support in the fact that the sensual pleasures generally recognised as greatest are those attending the activities of organs which are normally left unexercised for considerable intervals. Still, there are many facts that it does not explain--_e.g._ the great differences in the pleasures obtainable at any given time by different stimulations of the same sense; the phenomenon expressed in the proverbial phrase “L’appétit vient en mangeant”; and the fact that the exercise of the visual organs after apparently dreamless sleep does not give appreciably keener pleasure than it does at ordinary times. It would seem that we must seek for some special cause of the pleasurable effect of intermittence in certain cases. And this cannot be merely the greater intensity of the nervous action that takes place when long-unexercised and well-nourished nerve-centres are stimulated: for why, if that were the explanation, should the normal consciousness of full nervous activity, gradually attained--as when we are in full swing of energetic unwearied work of a routine kind--be often nearly or quite indifferent? Among the various competing hypotheses offered at this point of our inquiry--no one of which, I believe, has attained anything like general acceptance as covering the whole ground--I select for discussion one that has special ethical interest.