Food study

Undoubtedly some of the breaking down of the cellulose proceeds further than this, and hydrogen and other gases are produced which have no nutritive value. But not all forms of cellulose are easily enough broken down to have such changes occur. Cotton is a form of cellulose which would be absolutely without nutritive value. Such tender cellulose as is found in the cell walls of seeds like the cereals, and in vegetables, especially when young, is more capable of being digested. Still, it is probable that the less cellulose there is present in a vegetable food, the more digestible it is. This is probably the reason that rice is so easily digested, for it contains less cellulose than the other grains. Boiling in water does not change real cellulose at all, just as cotton clothes are not changed by boiling. But the cellulose cell walls of a plant are stiffened with other related substances ; for one, with the pectose which changes to pectin. Cooking dissolves out some of these intercellular substances and also hydrates the starch, and so cooked vegetables are softened. Then, as has already been explained, by thorough cooking the cellulose walls may be ruptured by the swelling of the starch grains within the cells and so the contents exposed without its being necessary first to digest the cell walls. Some authorities believe that inert particles like cellulose are sufficiently rough to stimulate the intestines to peristaltic action, that is, to movements which hasten the passage of food through the intestines and which are an aid in combating constipation. But, since foods are not laxative in proportion to the amount of cellulose they contain, others believe this action is due rather to the stimulus of certain salts which occur largely in the husks of the cereal ; and that it is due to the presence of these salts and not to the larger amount of cellulose in them that such articles of food as cracked wheat and graham bread are more laxative than those cereals which have undergone more extensive manufacturing processes. MINERAL AND ORGANIC SALTS 65 MINERAL AND ORGANIC SALTS Mineral matter occurs not only in the teeth and bones, but in every tissue of the body and in all the fluids. It is necessary in all the vital processes. The principal mineral elements in the body are calcium, magnesium, iron, sodium, potassium, phosphorus, chlorine, iodine, fluorine, silicon, and sulphur. These occur as compounds, forming both mineral and organic salts. Unlike carbohydrates, fats, and proteins, mineral salts are not changed in digestion nor are they oxidized, and so they do not furnish the body with energy. When organic matter is burned, these salts remain unconsumed as the ash. Mineral matter is present in all the digestive juices and plays its part in the digestion and absorption of foods. Mineral matter is dissolved in the blood and regulates its specific gravity and its alkalinity. It is found in all tissues, where it is concerned in metabolism.* Mineral matter, too, probably stimulates the contractions which cause the heart to beat.