While childhood is the conspicuous proof of the renewing of habit rendered possible by impulse, the latter never wholly ceases to play its refreshing rôle in adult life. If it did, life would petrify, society stagnate. Instinctive reactions are sometimes too intense to be woven into a smooth pattern of habits. Under ordinary circumstances they appear to be tamed to obey their master, custom. But extraordinary crises release them and they show by wild violent energy how superficial is the control of routine. The saying that civilization is only skin deep, that a savage persists beneath the clothes of a civilized man, is the common acknowledgment of this fact. At critical moments of unusual stimuli the emotional outbreak and rush of instincts dominating all activity show how superficial is the modification which a rigid habit has been able to effect. When we face this fact in its general significance, we confront one of the ominous aspects of the history of man. We realize how little the progress of man has been the product of intelligent guidance, how largely it has been a by-product of accidental upheavals, even though by an apologetic interest in behalf of some privileged institution we later transmute chance into providence. We have depended upon the clash of war, the stress of revolution, the emergence of heroic individuals, the impact of migrations generated by war and famine, the incoming of barbarians, to change established institutions. Instead of constantly utilizing unused impulse to effect continuous reconstruction, we have waited till an accumulation of stresses suddenly breaks through the dikes of custom. It is often supposed that as old persons die, so must old peoples. There are many facts in history to support the belief. Decadence and degeneration seems to be the rule as age increases. An irruption of some uncivilized horde has then provided new blood and fresh life--so much so that history has been defined as a process of rebarbarization. In truth the analogy between a person and a nation with respect to senescence and death is defective. A nation is always renewed by the death of its old constituents and the birth of those who are as young and fresh as ever were any individuals in the hey-day of the nation's glory. Not the nation but its customs get old. Its institutions petrify into rigidity; there is social arterial sclerosis. Then some people not overburdened with elaborate and stiff habits take up and carry on the moving process of life. The stock of fresh peoples is, however, approaching exhaustion. It is not safe to rely upon this expensive method of renewing civilization. We need to discover how to rejuvenate it from within. A normal perpetuation becomes a fact in the degree in which impulse is released and habit is plastic to the transforming touch of impulse. When customs are flexible and youth is educated as youth and not as premature adulthood, no nation grows old.