370 



BIOLOGY FOR BEGINNERS 



* S TO M AC H *~ 



Saliva. Saliva is a thin, alkaline fluid containing the enzyme 

 ptyalin, which changes starch to soluble sugar, but this action is 

 slight, since the food remains so short a time in the mouth. How- 

 ever, the other functions of saliva make it important that it be 

 thoroughly mixed with the food, since its presence in the stomach 

 stimulates the gastric glands. It also permits foods to be tasted, 

 since, only in solution will the food affect the nerves of this sense. 

 Furthermore, saliva aids in chewing and is indispensable in swal- 

 lowing food, so that its digestive function is only one of several, 

 and the quantity secreted is much greater than one might suppose, 

 being about three pints per day. 



The steps of the digestion process in the mouth, then, are 



1. Food mechanically crushed. 



2. Food moistened for taste and swallowing. 



3. Some starch changed to sugar*. 



4. Very slight absorption of sugar, water, salts. 



The Stomach. Passing 

 from the mouth, the food 

 enters the gullet, which at 

 a distance of about nine 

 inches enlarges into the 

 stomach. This organ is 

 located just beneath the 

 diaphragm with the inlet 

 at the left and close to the 

 heart. Except when fully 

 distended it is not the 

 smooth, pear-shaped organ 

 usually pictured, but may be collapsed and empty, or almost any 

 irregular shape, depending on its contents, and muscular move- 

 ments. 



Its function is very largely to store and finely divide the food. 

 We usually eat at one time enough food to last for several hours. 

 This food must be stored somewhere and the stomach provides 

 the place. Also, chewing has only partly divided the food, so a 

 second function of the stomach is to furnish the mechanical separa- 



Courtesy of Ginn and Company. 

 FIG. 118. From Hough and Sedgwick. 



