The pain arising from restricted activity can equally be explained in terms of movement. If we believe that our system has a limited amount of energy which—as long as life is maintained—must necessarily be active in some direction or other, then we shall also understand that anything which closes the natural and usual outlet of this energy will give rise to activities in related organs, the nutritive state of which does not present the conditions of pleasurable function. Mr. Marshall has tried to indicate the details of the transition by which inactivity in one organ causes excessive activity in other organs. His description of the “gorging of the nutritive channels,” “the calling for aid of the disabled elements,” etc., is, however, too figurative and poetical to be of any importance in a psychological argument.[55] Taken as a vague and necessarily coarse metaphor, this physiological image may, however, illustrate a process which perhaps can never be exactly analysed, but which is nevertheless familiar to everybody. No one who has experienced in any higher degree the diffused sensation of gnawing inactivity can doubt the active element in this corroding feeling. One seems to feel how the checked and thwarted impulses devouringly turn themselves inward. Poetical literature is full of passionate outcries against the tortures which imposed inaction inflicts on active spirits; and modern autobiographies give us pathetic examples of the sufferings of those whose intellectual activity has been diverted from outward aims to internal analysis. The candid confessions of Amiel and Kierkegaard show the inevitable necessity with which mental energy, if arrested in its natural course, finds itself an outlet in destructive activity. This truth had already been expressed in simple and drastic form in Logau’s old epigram:— Ein Mühlstein und ein Menschenherz wird stets herumgetrieben. Wenn beides nicht zu reiben hat, wird beides selbst zerrieben.