Further, a complete and ungraduated response to stimulus—­an “all-or-none reaction”—­is characteristic of the instinctive life and of the instinctive life alone.  Those whom it rules for the time give themselves wholly to it; and so display a power far beyond that of the critical and the controlled.  Thus, fear or rage will often confer abnormal strength and agility.  A really dominant instinct is a veritable source of psycho-physical energy, unifying and maintaining in vigour all the activities directed to its fulfilment.[74] A young man in love is stimulated not only to emotional ardour, but also to hard work in the interests of the future home.  The explorer develops amazing powers of endurance; the inventor in the ecstasy of creation draws on deep vital forces, and may carry on for long periods without sleep or food.  If we apply this law to the great examples of the spiritual life, we see in the vigour and totality of their self-giving to spiritual interests a mark of instinctive action; and in the power, the indifference to hardship which these selves develop, the result of unification, of an “all-or-none” response to the religious or philanthropic stimulus.  It helps us to understand the cheerful austerities of the true ascetic; the superhuman achievement of St. Paul, little hindered by the “thorn in the flesh”; the career of St. Joan of Arc; the way in which St. Teresa or St. Ignatius, tormented by ill-health, yet brought their great conceptions to birth; the powers of resistance displayed by George Fox and other Quaker saints.  It explains Mary Slessor living and working bare-foot and bare-headed under the tropical sun, disdaining the use of mosquito nets, eating native food, and taking with impunity daily risks fatal to the average European.[75] It shows us, too, why the great heroes of the spiritual life so seldom think out their positions, or husband their powers.  They act because they are impelled:  often in defiance of all prudent considerations! yet commonly with an amazing success.  Thus General Booth has said that he was driven by “the impulses and urgings of an undying ambition” to save souls.  What was this impulse and urge?  It was the instinctive energy of a great nature in a sublimated form.  The level at which this enhanced power is experienced will determine its value for life; but its character is much the same in the convert at a revival, in the postulant’s vivid sense of vocation and consequent break with the world? in the disinterested man of science consecrated to the search for truth, and in the apostle’s self-giving to the service of God, with its answering gift of new strength and fruitfulness.  Its secret, and indeed the secret of all transcendence is implied In the direction of the old English mystic:  “Mean God all, all God, so that nought work in thy wit and in thy will, but only God,"[76] The over-belief, the religious formula in which this instinctive passion is expressed, is comparatively unimportant The revivalist, wholly possessed by concrete and anthropomorphic ideas of God which are impossible to a man of different—­and, as we suppose, superior—­education, can yet, because of the burning reality with which he lives towards the God so strangely conceived, infect those with whom he comes in contact with the spiritual life.