When the control of instinct over life is gradually replaced by reason, this tendency to exercise gradually diminishes until it is often surprising to find how little people are taking. As it is mainly the need for exercise that forces people out into the air, indoor life comes to be the main portion of existence. This is all contrary to nature, and so it is not surprising that _disease_, in its original etymological sense of discomfort, develops rather readily. The lack of exercise in the air permits a great many people to drift into all sorts of morbid conditions in which they are quite miserable. This {135} is, of course, particularly true as regards nervous ailments of various kinds; only under the term nervous ailments should be included not alone direct affections of the nervous system or functional disturbances of nerves, but also a number of other conditions. Nervous indigestion, insomnia, neurotic constipation and many of the symptomatic affections associated with these conditions, tired feelings that interfere with activities, headache, various feelings of discomfort in the muscles and around the joints, inability to control the emotions and other such common complaints--if that is the proper word for them--all these are fostered by a sedentary life indoors. They frequently make not only the patient himself--or oftener herself--miserable, but also all those who come in contact with her. Above all, it must not be forgotten that lack of exercise in the open air has a very definite tendency to make people extremely sensitive to discomforts of all kinds, mental as well as physical. Many a man or woman whose life seems full of worries, sometimes without any adequate cause at all, who goes from one dread to another, who wakes in the morning with a sense of depression, find that most of these feelings and sometimes all of them, {136} disappear promptly when they begin to exercise more in the open. Nothing dispels the gloom and depressions consequent upon an accumulation of cares and worries of various kinds like a few weeks in the woods, where every moment is passed in the fresh outdoor air, which actually seems to blow the cobwebs of ill feelings away and leaves the individual with a freedom of mind and a comfort of body that he almost expected never to enjoy again.