We must first try to conceive the experiences of the soldier before the occurrence of the knock-out blow, so far as they bear on his present condition. Let us suppose that his period of training has made him physically and mentally fitter than he had ever been before, that no military causes of anxiety or fear, such as the experience or the anticipation of being torpedoed on the outward voyage, have operated to any noteworthy extent in his case. He enters the trenches in first-class condition. The duration of his stay there, provided he is not wounded, or attacked by any bodily illness, will depend from that time forward upon the nature, duration, intensity and frequency of the emotion-exciting causes, and upon himself. By that all-inclusive word “himself” we mean to signify chiefly his temperament, disposition and character.[6] It must be remembered that one of the greatest sources of breakdown under such circumstances is intense and frequently repeated emotion.[7] By this is meant not only experiences of fear or of sympathy with suffering comrades, in short, those conditions the manifestations of which might cause the man in the trenches to be spoken of as “emotional,” but also other mental states associated with general excitement, anxiety, remorse for major or minor errors, anger, elation, depression and that complex but very real state, the fear of being afraid. (The more definite terms of technical psychology are not used here, as it is considered wiser to employ popular language.) The soldier may be subjected to intense emotional stimuli of this kind for days or weeks without relief. And whereas to the mental sufferer in civil life sleep often is vouchsafed, “setting him on his feet” to continue, more or less effectively, the struggle next day, to the soldier sleep may be impossible, not necessarily because of his excited mental state, but simply from the lack of opportunity or the disturbances going on about him. In course of time this loss of sleep from external causes may easily set up bodily and mental excitability, which in its turn acts as a further cause of insomnia. The usual mental conditions associated with loss of sleep then rapidly supervene: pains and unpleasant organic sensations, hyperæsthesia, irritability, emotional instability, inability to fix the attention successfully upon important matters for any length of time, loss of the power of inhibition and self-control.[8] These symptoms, troublesome enough in civil life, become positively dangerous to the man in the trenches, especially if he is in a position of responsibility. In that case his standing as officer or N.C.O. merely adds to his mental distress. Bodily hardship, such as exposure to cold and wet, hunger, and the irritation from vermin, obviously aggravates the disorders we have described.