DIGESTION 131 



31. The Intestines. The intestines are continuous with the 

 stomach, and consist of a fleshy tube, or canal, twenty-five feet 

 in length. The small intestine, whose diameter is about one 

 inch and a half, is twenty feet long, and very winding. The 

 large intestine is much wider than the former, and five feet 

 long (Fig. 29). The general structure of these organs resembles 

 that of the stomach. Like it, they are provided with, a mucous 

 membrane, or inner lining, whence flow their digestive juices ; 

 and, just outside of this, a muscular coat, which propels the 

 food onward from one point to another. 



32. Moreover, both the intestines -and stomach are enveloped 

 in the folds of the same outer tunic or membrane, called the 

 peritoneum^ This is so smooth' and so well lubricated, that 

 the intestines have the utmost freedom of motion within 

 the abdomen. In the small intestines the work of digestion is 

 completed, the large intestine receiving from them the indi- 

 gestible residue of the food, and in time expelling it from the 

 bod} 



w 



Intestinal Digestion. As soon as the food passes the 

 [orus and begins to accumulate in the upper part of the 

 intestines, it excites the flow of a new digestive fluid, which 

 enters through a small tube, or duct, jibout three inches below 

 the stomach. It is formed by the union of two distinct fluids 

 the bile and the pancreatic juice. The bile is secreted by the 

 cells of the liver^ the largest gland of the body, situated on 

 the right side and upper part of the abdomen (Fig. 28). The 

 bile is constantly formed, but it flows most rapidly during 

 digestion. During the intervals of digestion it is stored in the 

 gall-bladder, a small membranous bag attached to the under 



Now set these three tubes aside in a warm place for a few hours, or 

 until the following day, when you will be able to demonstrate that in the 

 first two no change has taken place, while the white of egg in the third 

 has been entirely dissolved. 



31. What are the intestines? The small intestines? The large intestines? Their 

 structure ? 



32. Peritoneum ? The work of digestion ? 



33. The presence of food in the intestines ? Bile ? 



