IV. ABSORPTION is performed in two ways, by the _veins_, and the _lacteals_. (1.) The veins in the stomach [Footnote: The veins and the lacteals are separated from the food by a thin, moist membrane, through the pores of which the fluid food rapidly passes, in accordance with a beautiful law ("Popular Physics," p. 53) called the _Osmose_ of liquids. If two liquids of different densities are separated by an animal membrane, they will mix with considerable force. There is a similar law regulating the interchange of gases through a porous partition, in obedience to which the carbonic acid of the blood, and the oxygen of the lungs, are exchanged through the thin membrane of the air cells.] immediately begin to take up the water, salt, grape sugar, and other substances that need no special preparation. The starch and the albuminous bodies are also absorbed as they are properly digested, and this process continues along the whole length of the alimentary canal. In the small intestine, there is a multitude of tiny projections (_villi_) from the folds of the mucous membrane, more than seven thousand to the square inch, giving it a soft, velvety look. These little rootlets, reaching out into the milky fluid, drink into their minute blood vessels the nutritious part of every sort of food. (2.)The lacteals [Footnote: From _lac_, milk, because of the milky look given to their contents by the chyle.] (p. 126), a set of vessels starting in the villi side by side with the veins, absorb the principal part of the fat. They convey the chyle through the lymphatics and the thoracic duct (Fig. 43) to the veins, and so within the sweep of the circulation. The Portal Vein [Footnote: So named because it enters the liver by a sort of gateway.] carries to the liver the food absorbed by the veins of the stomach and the villi of the intestines. On the way, it is greatly modified by the action of the blood itself. In the cells of the liver, it undergoes as mysterious a process as that performed by the lymphatic glands, and is then cast into the circulation. [Footnote: In these cells, the sugar is changed into a kind of starch called _glycogen_. This is insoluble, and so is stored up in the liver, and even in the substance of the muscles, until it is needed by the body, when it is once more converted into soluble sugar and taken up by the circulation. The liver also changes the waste and surplus albuminous matter into bile, and into urea and uric acid--the forms in which nitrogenized waste is excreted by the kidneys.] The food, potent with force, is now buried in that river of life from which the body springs momentarily afresh.