Foods are cooked to make them more digestible and to develop their flavor, so that they will taste better. Cooking also kills germs and parasites that might be harmful. Meats should be cooked rapidly on the outside to coagulate the surface albumen and keep in the juices. The heat, besides coagulating the albumen, turns the tough parts to gelatine. In cereals the tough envelope of cellulose is broken up and in vegetables the tough fibrous parts are softened and made more digestible. =The Liver.=--Below the diaphragm on the right and extending across above the stomach, resting in a way upon the transverse colon and the small intestine, is the liver, the largest gland in the body. It is dark reddish-brown in color and is larger in proportion in the child than in the adult. The upper surface is convex and lies in contact with the diaphragm, while the lower surface is concave to fit over the organs beneath. With a full breath it comes downward and forward, with the edge against the abdominal wall, and can be easily felt. Numerous strong ligaments, including the suspensory ligament from the diaphragm, hold it in place, and it is more firmly fixed than any other of the abdominal organs, probably on account of its large size. It is divided by fissures into five _lobes_, of which the most important are the right and left, the right one being the largest and containing the gall-bladder in one of its fissures. [Illustration: FIG. 56.--The liver, seen from below. 1, Inferior vena cava; 2, gall-bladder. (Morrow.)] The liver tissue contains a large number of _cells_ collected into _lobules_, in the center of each of which is a blood-vessel, the _intralobular vein_, from which a network of capillaries extends to the edge of the lobule, there being a capillary on either side of each row of cells. Between the cells also are the _intercellular biliary passages_, roots of the bile ducts which exist in the connective tissue between the lobules and which join to form two main ducts, one from the right and the other from the left lobe. By the union of these two ducts the _hepatic duct_ is formed, which, after a course of one or two inches, joins the cystic duct from the gall-bladder to form the _ductus communis_ or _common bile duct_. The liver has a double _blood supply_, the _hepatic artery_ from the celiac axis bringing nourishment to the connective tissue and the walls of the blood-vessels, while the capillaries between the cells come from the _portal vein_, which, being formed by the junction of the superior and inferior mesenteric, the splenic and the gastric veins, contains the proteins and carbohydrates absorbed during digestion. After its passage through the liver this blood from the portal vein is collected once more into the hepatic veins, which convey it to the inferior vena cava. During its passage, however, various changes take place, for the liver plays an important part in the metabolic processes of the body.