The muscles play an important part in the use of foods. Most of the heat is generated in them, by the sugar and fats coming in contact with the oxygen in the blood. This heat is liberated during every moment of the twenty-four hours, asleep or awake. Of course, more is liberated during exercise, since the movement of the muscles sets all tissues into activity and the blood circulates more strongly, bringing a greater supply of oxygen to them. It is always well during active exercise to stop frequently and fully inflate the lungs. The effort should always be made to breathe fully and deeply—otherwise the pressure of the liberated carbon dioxid will cause a pressure throughout the blood stream, particularly about the heart and in the head. This pressure is relieved when the excess of carbonic acid gas liberated has been thrown off by the lungs. Nature makes the effort to throw off the excess of carbonic acid gas by forcing one to breathe more rapidly while running or taking unusual exercise.
The oxidation changes are simply a combustion of sugars and fats, liberating latent heat as they are brought into contact with the oxygen. Exercise and a regulation of the amount of carbohydrates and fats consumed in the foods is the natural, scientific method for the reduction of an excess of fat.
A certain amount of protein is constantly oxidized in the muscles, also, being broken down into carbon dioxid, water and a number of nitrogenous mid-products. The carbonic acid gas and water are thrown off by the lungs and the partially oxidized, nitrogenous waste is carried to the liver, where it is further oxidized and prepared for excretion, through the kidneys, lungs, skin and intestines.
When sugar is carried to the muscles in larger quantities than can be utilized by them, it is often built up into animal starch and stored in the form of glycogen, similar to its chemical change and storage in the liver.
This storage of glycogen in the muscles and in the liver is a wise provision of Nature. It is a reserve to be called upon whenever the expenditure of heat and energy exceeds the amount supplied in any day’s rations.
Work of the Nerves
The nerves oxidize food materials, but not to any great extent, excepting during nervous activity. During periods of rest, food materials are stored in the nerve cells in grandular form. They represent concentrated nerve foods and are the result of anabolic processes. During nervous activity they are oxidized and carried away through the blood and the lymph. This oxidation of the food, stored in the nerves, creates nervous energy and heat.
The energy liberated by the nerves resembles electrical energy.
Where one subjects himself continuously to an excess of nervous activity, all reserve food material, stored in the nerve cells, is used and the result is a trying nerve tension. Such individuals need plenty of easily digested food.