306 DIGESTION AND ABSORPTION 



Fats, which so far have been unchanged except to be melted by the 

 heat of the body, are changed by the action of the pancreas into 

 a form whicli can pass through the wails of the food tube. If we 

 test pancreatic fluid, we find it strongly 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 emulsion. Pancreatic 

 fluid similarly emulsifies fats and changes them into soft soaps and 

 fatty acids. Fat in this form may be absorbed. The process of 

 this transformation is not well understood. 



Conditions under which the Pancreas does its Work. — The 

 secretion from this gland seems to be influenced by the overflow of 

 acid material from the stomach. This acid, on striking the lining 

 of the small intestine, causes the formation in its walls of a sub- 

 stance known as secretin. This secretin reaches the blood and 

 seems to stimulate all the glands pouring fluid into the intestine 

 to do more work. A pint or more of pancreatic fluid is secreted 

 every day. 



The Intestinal Fluid. — Three different pancreatic enzymes do 

 the work of digestion, one acting on starch, another on protein, and 

 a third on fats. It has been found that some of these enzymes will 

 not do their work unless aided by the intestinal fluid, a secretion 

 formed in glands in the walls of the small intestine. This fluid, 

 though not much is known about it, is believed to play an important 

 part in the digestion of all lands of foods left undigested in the 

 small intestine. 



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 

 alkahne fluid of greenish color. It reaches the intestine through 



