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The hemoglobin molecule (part of the red blood cell) is responsible for carrying most of the oxygen. Carbon dioxide, a waste product of cell metabolism, dissolves principally in the plasma. Hyperventilation occurs when one breathes too fast. This lowers the carbon dioxide level of the blood, producing several uncomfortable symptoms. Tingling, drawing of the hands, and dizziness can occur. These may be relieved after a short period of shallow breathing into a paper bag, quickly reversing the abnormal gas exchange in the tissues. Breathing, furthermore, involves the brain, skeletal muscles, and even some bones. Ordinarily we take about a pint of air into our lungs with each breath. This is referred to as the tidal volume. The largest amount of air that we can breathe in and out in one full inspiration is known as the vital capacity. In most adults this amounts to approximately 4.5 to five quarts (or liters). A special diagnostic device, called the spirometer, is used to measure the amount of air exchanged in breathing. THE CIRCULATION Scriptures declare that “the life of the flesh is in the blood,” (Leviticus 17:11). However, without the circulation of blood, life as we know it, would be impossible. As we consider the circulatory system, let’s look first at the blood and its constituent elements. Our survey of clotting factors and blood types will be followed by a close look at the heart, the blood vessels and their vital functions. Approximately four to five quarts of blood constantly circulate in an average man or woman. The time required for our blood to traverse throughout the entire system can be measured. When a bitter substance, such as bile, is injected into a vein of the arm, it can make its circuit through the heart, the lungs, back to the heart, then be tasted by the tongue, all within 10 to 15 seconds! So, it is no wonder that each hormone produced by the body, every morsel we eat, and all the oxygen inhaled are all rapidly distributed throughout the body. When blood is centrifuged or allowed to stand for several hours, it normally separates into two distinct layers. There is a layer of blood cells that settles first, being heavier than the plasma, which is primarily fluid. If we first allow the blood to clot, then separate the liquid portion, we have serum, which is basically blood plasma minus the clotting factors. This ratio of blood cells to plasma is measured in the laboratory with the hematocrit test. A small capillary tube of blood is centrifuged. Allowing for slight variations between men and women, the blood cellular elements will usually constitute 38 to 46% of the total volume. Lesser figures indicate the presence of anemia.