372 



BIOLOGY FOR BEGINNERS 



1. The fats all unchanged. 



2. Most of the carbohydrates. 



3. A large portion of the proteids. 



4. Some sugars, peptones and water, which were not absorbed 

 in the stomach. 



It is evident that, so far, the food has been mainly prepared for 

 digestion rather than digested, a process that is chiefly accom- 

 plished in the small intestine. 



The Intestine. The stomach connects with the small intestine 

 by way of a muscular valve (the pylorus) which prevents the food 



from passing before it is 

 thoroughly broken up in the 

 stomach. 



The intestine is the most im- 

 portant portion of the digestive 

 tract, and consists of a coiled 

 tube about twenty-five feet in 

 length. The part next the 

 stomach is about twenty feet 

 long, about one inch in diameter 

 and is called the small intestine, 

 while the remaining five feet are 

 over two inches in diameter and 

 are called the large intestine. 



FIG. 120. Mucous membrane of 

 the small intestine of the dog. A, 

 artery; B, vein; C, capillaries; D, 

 lacteals; E, glands of Lieberkiihn; 

 Ep., epithelial tissue. After^Cadiat. 

 See Kellogg. 



The small intestine joins the 

 large at the lower, right side of 

 the abdomen, and at this point 

 is the location of the appendix. 

 Inflammation of this organ is called appendicitis. 



Adaptations for Increase of Surface. In order that both secre- 

 tion of fluids and absorption of food may go on, much surface (for 

 osmosis) is required. 



For this increase of surface, the intestine is adapted in three 

 ways: 



1. Its great length and coiled position in the body. 



2. Its inner lining projects in creases and folds. 



