Do not consider this a "health exercise"; _never take health exercises, or do gymnastics to make you well. To do so is to recognize sickness as a present fact or as a possibility, which is precisely what you must not do_. The people who are always taking exercises for their health are always thinking about being sick. It ought to be a matter of pride with you to keep your spine straight and strong; as much so as it is to keep your face clean. Keep your spine straight, and your chest full and flexible for the same reason that you keep your hands clean and your nails manicured; because it is slovenly to do otherwise. Do it without a thought of sickness, present or possible. You must either be crooked and unsightly, or you must be straight; and if you are straight your breathing will take care of itself. You will find the matter of health exercises referred to again in a future chapter. It is essential, however, that you should breathe AIR. It appears to be the intention of nature that the lungs should receive air containing its regular percentage of oxygen, and not greatly contaminated by other gases, or by filth of any kind. Do not allow yourself to think that you are compelled to live or work where the air is not fit to breathe. If your house cannot be properly ventilated, move; and if you are employed where the air is bad, get another job; you can, by practicing the methods given in the preceding volume of this series--"THE SCIENCE OF GETTING RICH." If no one would consent to work in bad air, employers would speedily see to it that all work rooms were properly ventilated. The worst air is that from which the oxygen has been exhausted by breathing; as that of churches and theaters where crowds of people congregate, and the outlet and supply of air are poor. Next to this is air containing other gases than oxygen and hydrogen--sewer gas, and the effluvium from decaying things. Air that is heavily charged with dust or particles of organic matter may be endured better than any of these. Small particles of organic matter other than food are generally thrown off from the lungs; but gases go into the blood.