All starches must undergo much chemical change by action of the saliva, the intestinal juice and by the liver, before they can be used by the body. They are first converted into dextrine and then into maltose (animal sugar). The digestion is begun by the saliva in the mouth and continued in the stomach by the saliva swallowed with the food. If the saliva fails to digest all of the starch, either in the mouth or the stomach, it passes unchanged into the intestines, where it is converted by the amylase of the intestinal juice, first into dextrine and then into maltose, or sugar. It is absorbed into the blood as sugar. After the digested starch (maltose) passes into the blood it is spoken of as sugar. Before it is converted into energy it is again changed in the liver into animal starch (glycogen) and stored for a time in the liver. When the system is ready for it, it is again broken down into sugar, because in the form of glycogen it cannot be absorbed into the blood. The chemical process used in the formation of glucose, from the starch in corn, is allied to the change in the liver, from starch into sugar. The starches and sugars are really the “reserves” or “go-betweens” of the body, being stored until needed. If starches are consumed in unduly large quantities, without sufficient exercise to burn them up, they overload the liver and clog the system. Starchy foods should not be given to children before the starch converting ferments are formed, nor to one in disease where these ferments are interrupted. Nitrogenous Foodstuffs or Proteins The proteins form heat and energy when the supply of sugars, starches, and fat are exhausted, but proteins, alone form muscle, bone and sinew. They are, in this sense, the most important of foods,—they are, also, the most costly. The foods most rich in proteins are meat and eggs. These have undergone chemical changes from the vegetable kingdom being built up into more complex compounds in the animal kingdom. Meat and eggs are the tissue builders. In this connection it may be well to state that blood is tissue; thus meat and eggs build the blood, as well as muscle and sinew. Nitrogenous foods, or proteins, are so called because of the large proportion of nitrogen which they contain. All nitrogenous foods contain considerable carbon—mostly in the form of fat in the meat elements—but the carbonaceous foods contain so little of the proteins that they do not appreciably enter into the nutrition,—the carbon and nitrogen in the carbo-nitrogenous foods are more equally divided. The nitrogenous or protein elements in the body constitute about one-fifth of its weight. They make the framework, forming the basis of blood, lymph, muscle, sinew, bone, skin, cartilage, and other tissues. Worn out body tissues is constantly being torn down and eliminated and the protein in the foods must daily furnish material for repair, as well as for building new tissue in the growing child.