Page:First course in biology (IA firstcourseinbio00bailrich).pdf/573

 breaks up the fats into tiny globules. Fat in small globules floating in a liquid is called an emulsion; fresh milk is an emulsion of cream (Fig. 98). Fat is not changed to another substance by digestion, but it is emulsified, and in this condition it readily passes through the walls of the intestines and is absorbed by the lymphatics called lacteals (colored Fig. 5) found in the villi. It then ascends through the thoracic duct to a large vein at the left side of the neck (Fig. 100). The digested proteid, starch, and sugar pass into the capillaries of the portal vein, and go to the liver on their way to the general circulation (Fig. 100). The portal circulation empties into the large ascending vein leading to the right auricle (Fig. 100).

The Liver.—This large, chocolate-colored gland is located just beneath the diaphragm on the right side (Fig. 90, colored Fig. 6). It is on a level with the stomach, which it partly overlaps in front. The liver has three important functions: (1) It is a storeroom; digested sugar and starch are stored in it as a substance called liver starch (or glȳ'cogen). (2) It is a guardian, and destroys poisonous substances which may be swallowed, and which would otherwise enter the blood. Twice as much morphine or other poison is necessary to kill a man when it is taken by the mouth and passes through the liver as when it is injected through the skin. Alcohol, morphine, coffee, and drugs are partly burned up in the liver. (3) It is a gland, and secretes bile. The bile is made chiefly from waste products and impurities in the