The feeling of freshness these exercises will impart, the increased vigor and the enhanced clearness of mind that will come to you, will prove a grateful source of surprise. Many men, formerly in the habit of visiting for a cocktail, take a few deep breaths in this scientific manner. They claim that this Fresh Air Cocktail is better than any coffee or liquor stimulant. And it can be certain that nothing but good effects can ever follow it. By this system of breathing you can build up a wonderful physique. You can become strong and active, and have a superabundance of health and vitality--and without spending more than a few minutes a day at your breathing exercises. After a short time the _habit_ for slow, deep breathing is formed, and as with all habits, it requires no attention whatsoever. Hints for Controlled Breathing It should go almost without saying that to get the _best_ effects from air you should breathe the purest air obtainable. Air which is full of dust particles, for instance, may be actually irritating to the delicate mucous membrane that lines the nose, throat, bronchial tubes and air cells of the lungs. This dust contains particles of organic matter derived from the excrement of horses and dogs, from dried atoms of offal and decaying vegetable matter, or from dried mud impregnated with urine. Indeed, it is very largely upon these particles that the micro-organisms--arch enemies of mankind as well as of animal kind--are carried on their errand of destruction. These micro-organisms are most abundant in the air of inhabited rooms--and the more people in the room the greater the number of microbes present. So don’t be afraid of open windows--day or night. Remember Florence Nightingale’s quaint observation, “Windows are made to be opened.” Always Breathe Through the Nose It should be remembered, also, that so far as possible, all inhalation of air should be through the nose. This is for two very important reasons. First, the fine hairs lining the nasal passages act as a sieve through which the inspired air is strained. Further than this the lower turbinated bodies in the nose, and the lower half of the middle turbinates are covered with tiny cells (ciliated tissue) protruding from the membrane covering of the turbinates. These cells catch and hold any particles of dust or other matter that may have slipped through the hair screen of the nostrils. Thus dust, germs and other harmful material are removed from the air currents, and prevented from reaching the lung cells. The next most important reason is that the chambers of the nose, with their wonderfully rich blood supply, act as temperature regulators. If you breathe air at zero temperature through the nose it is actually warmed to body temperature before it passes into the bronchial tubes.