DIGESTION. 9 



in the mucous membrane lining the stomach. Others, like tartar 

 emetic, apomorphine, etc.., attain the same results by reason of their 

 stimulating the vomiting center in the medulla. 



DIGESTION IN THE INTESTINES. 



When the food is converted into chyme and partially dissolved 

 by the gastric juice, it passes into the small intestine, where it is 

 subjected to new reagents : the bile, pancreatic juice, and intestinal 

 juices. Here the food is prepared for absorption, forming what is 

 called chyle, which is rapidly taken up by the chyliferous vessels. 



Because of the small and large calibers of the two parts of the 

 intestinal tract, the portions have received the names of small and 

 large intestines, respectively. The small intestine, the continuation 

 of the stomach, opens into the large intestine by an orifice which is 

 guarded by the ileo-ccecal valve. Under ordinary and normal condi- 

 tions this valve allows the passage of the remnants of active digestion 

 to pass through from the small into the large intestine; very rarely 

 does the reverse occur, except in some cases of hernia and other ob- 

 structions in the large intestine. 



THE SMALL INTESTINE. 



This tube is cylindrical and much convoluted. It occupies the 

 umbilical region and is suspended from the vertebral column by the 

 mesentery. It measures about twenty-five feet in length, and its 

 diameter is about one and three-fourths inches. As it continues to 

 join the large intestine it becomes slightly narrower. It consists of 

 three parts: the duodenum, jejunum, and ileum. 



The duodenum is twelve fingers' breadth in length, and it is 

 the widest part of the small intestine. It commences at the pyloric 

 end of the stomach and opposite the second lumbar vertebra; it 

 terminates in the jejunum. The common bile-duct and the pan- 

 creatic duct perforate the inner side of the duodenum. 



The jejunum constitutes about two-fifths of the small intestine. 

 It is wider than the ileum and is characterized by the absence of the 

 agminated glands. The ileum constitutes three-fifths of the small 

 intestine, and terminates in the right iliac region by joining the large 

 intestine at a right angle. 



