360 DIGESTION AND ABSORPTION 



alkaline in its reaction. If two test tubes, one containing olive oil 

 and water, the other olive oil and a weak solution of caustic soda, 

 an alkali, be shaken violently and then allowed to stand, the oil 

 and water will quickly separate, while the oil, caustic soda, and 

 water will remain for some time in a milky emulsion. If this 

 emulsion be examined under the microscope, it will be found to 

 be made of millions of little droplets of fat, floating in the liquid. 

 The presence of the caustic soda helped the forming of the emul- 

 sion. Fat in this form may be absorbed. Pancreatic fluid simi- 

 larly emulsifies fats and changes them into soft soaps and fatty 

 acids. The process of this transformation is not well understood. 



Liver. The liver is the largest gland in the body. In man, it hangs 

 just below the diaphragm, a little to the right side of the body. During life, 

 its color is deep red. It is divided into three lobes, between two of which 

 is found the gall bladder, a thin-walled sac which holds the bile, a secretion 

 of the liver. Bile is a strongly alkaline fluid of greenish color. It reaches 

 the intestine through a common opening with the pancreatic fluid. Al- 

 most one quart of bile is passed daily into the digestive canal. 



Functions of Bile. The action of bile on foods is not very well 

 known. It is slightly antiseptic, and thus may prevent fermenta- 

 tion within the intestine by destroying bacteria. It also has the very 

 important faculty of aiding the passage of fats through the walls of 

 the intestine. If two funnels, each containing filter paper, one 

 moistened with bile, the other dry, be filled with oil, the oil will be 

 found to pass through the moistened funnel with much greater ease. 



Formation of Glycogen. Perhaps the most important func- 

 tion of the liver is the formation within it of a material called glyco- 

 gen, or animal sugar. The liver is supplied by blood from two 

 sources. The greater amount of blood received by the liver comes 

 directly from the walls of the stomach and intestine to this organ. 

 It normally contains about one fifth of all the blood in the body. 

 This blood is very rich in food materials, and from it the cells of 

 the liver take out sugars to form glycogen. 1 Glycogen is stored 

 in the liver until such a time as a food is needed that can be quickly 

 oxidized ; then the glycogen is carried off by the blood to the tissue 



1 It is known that glycogen may be formed in the body from proteid, and possibly 

 from fatty foods. 



