I cannot too strongly emphasize the importance of walking alone, for it is then that you shift your nerve energy from the dry cell battery of the brain to the magneto, which is the spinal cord. The spinal cord works automatically and it doesn't wear itself out. The brain tires if it uses its energy. In walking you use the thought and the brain impulse to start the magneto, and then the spinal cord action is automatic. This automatic action of the spinal cord is a wise provision of nature to conserve strength. The spinal cord energy is what you might call automatic habit. For instance, in dressing and undressing yourself, you will recall that you put on or take off your clothes in regular order without giving the matter any thought. It is just habit. If you wish to demonstrate the difference between the control of the physical body by brain impulse, and the spinal cord impulse, try this some morning: Start out for your exercise and mentally frame sentences like this as you walk--"right step, left step, right step, left step," and so on. Give thought to each step you have taken, and notice how tired you will be when you have gone half a mile. The next morning, start to walk naturally; give no thought to walking; keep your mind on the beauties of nature which you are passing, or indulge in pleasant soliloquy, and you will feel no fatigue. There isn't a bit of theory in this chapter; it is positive, practical sense that I have proved by my own experiences and by the experiences of everyone to whom I have made this suggestion of walking alone. The moral is this--walk every morning and walk ALONE. 22. The body is made up of billions of little cells. These individual cells are in a state of perpetual activity. They exhaust, wear away, break down with work, and rebuild on food and rest. Every process of life--the beat of the heart, the throb of the brain in thought, the digestion of food, the excretion of waste--all are due to the activity of groups of highly specialized individual cells. [Sidenote: Body Waste.] Every cell uses up its own material and throws off poisonous by-products during activity. These by-products, or wastes, are very poisonous to the individual cell as well as to the entire organism. To get rid of this waste is one of the first duties of the system. It is with the body, made up of its countless millions of individual cells, just as it is with a city and its myriad people: the sewage of the community must be collected and disposed of. The city forms its poisons which we call sewage and the body its poisons, which we call excreta (or carbonic acid, urea, uric acid, faeces, etc.). It is no more important for a city to gather up and get ride of its poisonous sewage than for the animal organism to collect and excrete its cell-waste. Hence, the importance of maintaining normal and constant elimination throughout the body. [Sidenote: Health's Safety-First.]