It is in the crowded life of cities that these difficulties most beset the problem of how to bring health within the reach, not of course of those who suffer from definite disease, for that is the work of doctors and physicians, but of those who in surroundings which suited them would naturally be healthy. Hard brain-work, for instance, especially in a dead and vitiated atmosphere, though it produces merely headache in some, produces in many others (both the present writers are cases in point) violent appetite, and the natural impulse is to take large quantities of solid food. The result of this would of course be extreme somnolence, and a subsequent awakening from a sleep that is as different from nature-demanded sleep as is light from darkness, with an extreme attack of general inability. Now such a meal as this, which produced in the brain-worker somnolence and inability, would very likely have produced in the man who was shooting all day nothing but an added zest for his sport. In the one case the food goes, so to speak, to the right place; in the other to the wrong one. Yet how comparatively few of us study our health even in so superficial a manner as to know that appetite, when one lives in abnormal conditions, is not by any means the same thing as appetite when one lives wholesomely in the open air. And how many fewer have the sense, even if they know it, to put the lesson into practice, and deliberately alter their diet to suit the conditions under which they are bound to live. Again, there are many who, when able to take exercise, are healthy and fit for any work that they may have to do, in whom the difficulty, almost the impossibility, of getting it in the ordinary way in towns, produces a marked decline in health and consequently in output of work. Here, in a chapter devoted to the consideration of the question as applied to those who must live in towns, we shall discuss the possibility of athletic clubs to be brought within the means of those to whom such clubs as at present exist are not, by reason of expense and other causes, in any way accessible. For all these, also, we shall suggest such daily exercises as can be taken in a minimum of time in the minimum of space, which have for their object not the acquisition of huge muscles, but the acquisition of healthy nerves and muscles, prompt to obey, and swift to act. For these, too, as indeed for everyone, certain perfectly simple hints will be given about the use of air, and how to breathe properly, the use of water, warm to cleanse, hot or cold to brace, and hot vapour baths to counteract that persistent clogging of the passages of the skin which more particularly besets those whose life is passed in towns, where there is less air, less exercise, more dirt, and a tendency in all to indulge excessively (considering the conditions) in food and stimulants.