The lymph carries all of the food elements, therefore the protein, the fat, and the carbohydrate reach the tissues at the same time. If the fat and carbohydrate predominate, their excess serves to keep a portion of the protein away from the cells. The cells can use carbohydrate more easily than fat, so the surplus amount of carbohydrate is first used to produce energy. This spares the protein which is held in reserve for tissue repair, and the fat, being least readily used, is stored. When the carbohydrates and fats are not supplied, or when the system fails for any reason to appropriate those eaten to its use, the protein is used for heat and energy instead of being used for tissue building. If the demand, either in mental or physical energy, exceeds the daily supply for long, the body becomes lean. In order, therefore, to maintain a perfect equilibrium the supply of protein, carbohydrate, and fat should bear the proper relation, any excess at one time being equalized at another. If an overhearty meal is eaten the next should be light. Fat is harder to burn than the starches and sugars so that they are acted on first as an economy of effort, and the fat is held in reserve until the carbohydrates are exhausted. If one is cold, the quickest way to get warm is to generate more heat within by “turning on the draught,” or, in other words, by _breathing in more oxygen_. If cold, one should depend more on the oxygen within than on extra clothing. So many people put on more clothing to conserve the body heat and forget to generate more heat by arousing the fires within. This is like covering a dying fire, instead of turning on the draught to create more combustion. The carbon in the body is burned by being brought into contact with oxygen in the blood through exercise and full breathing, just as a fire is fanned to flame by bringing oxygen in contact with the fuel, by means of a draught of air. Keep all air away from a fire and it “dies out,” it has exhausted the oxygen and no heat is produced; keep all air from within the body, by cessation of breathing, and it also dies. A room is heated with difficulty if the air in it does not contain sufficient oxygen. Just so the body which is not constantly supplied with pure air generates very little heat. The effect of oxygen in the creation of heat is practically demonstrated by voluntary, rapid, deep breathing, completely filling the lungs with air, while out in the cold. The body will become quickly warmed on the coldest day by this practice. Ten to twelve deep breaths in succession “turn on the draught” inside and create combustion (heat), just as opening the draught to a stove by causing more air to circulate within it increases combustion or heat. Remember that heat is the result of combustion—the more rapid the combustion in the body, caused by oxygen breathed in through the lungs, the greater the heat.