The emotional tension to which one ordinarily refers as zest, enthusiasm, or interest, keeps up a certain vegetative tonus, a certain balance in the sympathetic adrenal and parasympathetic insular tonus. This effect is qualitatively similar to that of fear and rage, but less intensive and more prolonged. Fatigue and apathy developing during routine activity without interest are not merely subjective emotional states but are based on the lack of adaptation of carbohydrate metabolism. The emotional flight reaction is called by the authors 'vegetative retreat'. The inability of the organism to raise the sugar concentration of the blood as required during activity is the immediate cause for the feeling of fatigue. This view accounts fully for the beneficial effect of atropine and of a diet containing complex carbohydrates.