As the food is absorbed through the walls of the alimentary canal, it is picked up by the rootlets of the mesenteric veins[5] and by the lymph channels,—the latter, through the abdominal cavity, are called lacteals. Nearly all of the fats are absorbed through the lacteals. The whitish color given to the contents of the lacteals, by the saponified fats, gives rise to the term lacteal, meaning “whitish.” Nearly all of the proteins and sugars pass through the mesenteric veins and the portal veins into the liver. Here the sugars are at once attacked by the liver cells and built up into glycogen as described on page 81 and the proteins are passed through the liver into the arterial blood stream. A small portion of the proteins, however, do not go to the liver, but are passed directly into the lymphatics and thus into the blood stream, where they are again carried to the liver. To sum up,—the larger part of the absorption of sugars, starches, proteins, and fats is through the small intestine, though some are absorbed in the stomach and a very little through the large intestine; while some water and salts are absorbed in the stomach and small intestine, these are largely absorbed in the large intestine. FOOTNOTES: [3] A knowledge of the mucous lining of the stomach and intestines, and of the tributary glands, such as the liver and pancreas, is important to a thorough understanding of digestion, and the reader is referred to “The Vital Organs: Their Use and Abuse” of this series. This takes up the study of the secretion of digestive juices, the conditions favoring normal secretions, etc. [4] See “The Vital Organs; Their Use and Abuse” by Susanna Cocroft. [5] For illustration see the frontispiece of “The Circulation, Lungs, Heart,” of this series. The Work of Various Organs Affecting Digestion The purpose of this chapter is to show the work of other organs than the digestive organs in converting the digested food to use in the body, in tearing down waste, and in eliminating waste and an excess of material above the body needs. * * * * * [Sidenote: Work of the Liver] The liver is commonly called the chemical work-shop of the body. The proteins and sugars are carried through the blood (portal veins) to the liver directly they are absorbed from the alimentary canal. As the food materials filter through the blood capillaries, between the liver cells, several substances are absorbed, particularly sugar, which is here changed into animal starch called _glycogen_. It is held in the liver for a few hours in the form of glycogen and then redigested by the action of an amylolitic ferment and again gradually given out into the blood in the form of sugar; hence sugar is subject first to the anabolic change of being built up into glycogen, and then to the catabolic change of oxidation and breaking down.