Hydrogen and oxygen combined form water, hence we find from the above calculation that about three-fifths of the body is composed of water. Carbon is a solid: diamonds are nearly pure carbon; "lead" of lead pencils, anthracite coal and coke are impure forms of carbon. Carbon combined with other elements in the body makes about one-fifth of the whole weight. Carbon with oxygen will burn. In this way the carbon taken into the body as food, when combined with the oxygen of the inhaled air, yields heat to keep the body warm, and force--muscular strength--for work. The carbonic acid (or carbon dioxide) is given out through the lungs and skin. In the further study of carbonaceous foods, their relation to the body as fuel will be more clearly understood, as carbon is the most important fuel element. Phosphorus is a solid. According to the table, about one pound six ounces would be found in a body weighing 148 pounds. United with oxygen, phosphorus forms what is known as phosphoric acid; this, with lime, makes phosphate of lime, in which form it is found in the bones and teeth; it is found also in the brain and nerves, flesh and blood. Hydrogen is a gas, and like carbon unites with the oxygen of the inhaled air in the body, thus serving as fuel. The water produced is given off in the respiration through the lungs and as perspiration through the skin.[3] Calcium is a metal. The table given allows three pounds of calcium; united with oxygen, calcium forms lime. This with phosphoric acid makes phosphate of lime, the basis of the bones and teeth, in which nearly all the calcium of the body is found. The elements which bear no direct relation to the force production of the body, but which enter into tissue formation, are chlorine, sulphur, iron, sodium, potassium, phosphorus, calcium and magnesium. Bone tissue contains about 50 per cent. of lime phosphate, hence the need of this substance in the food of a growing infant, in order that the bones may become firm and strong. Lack of iron salts in the food impoverishes the coloring matter of the red blood corpuscles on which they depend for their power of carrying oxygen to the tissues; anaemia and other disorders of deficient oxidation result. The lack of sufficient potash salts is a factor in producing scurvy, a condition aggravated by the use of common salt. A diet of salt meat and starches may cause it, with absence of fresh fruit and vegetables. Such illustrations show the need of a well-balanced diet. In order to understand the value of the various classes of food and their relation to the body as force producers, tissue builders, etc., the following table may prove helpful:--