336 



HUMAN PHYSIOLOGY 



Inside of the stomach and intestine, show- 

 ing the folds of the mucous membrane. 



the heart and lungs from the 

 other organs of the body cavity. 

 The stomach is a pear-shaped 

 organ capable of holding about 

 three pints. The end opposite to 

 the gullet, which empties into 

 the small intestine, is provided 

 with a valve called the pylorus. 



Demonstration — Open the stom- 

 ach of the frog; remove its contents 

 by carefully washing. The stomach 

 wall is seen to be thrown into folds 

 internally. 



Gastric Glands. — Between these folds, in the stomach of man 

 as well as in the frog, are located a number of tiny pits. These 

 form the mouths of the gastric glands, which pour into the stomach 

 a secretion known as the gastric juice. The 

 gastric glands are little tubes, the lining of which 

 secretes the fluid. This fluid is largely water. 

 It is slightly acid in its chemical reaction. (It 

 contains about .2 per cent free hydrochloric acid.) 

 It also contains a very important enzyme called 

 pepsin, and another less important one called 

 rennin. 



The action of gastric juice upon proteids may be de- 

 termined by the following experiment. Number five 

 test tubes, 1 to 5 inclusive. 



In No. 1 place minced white of egg + water. 



In No. 2 place minced white of egg + .2 per cent 

 hydrochloric acid. 



In No. 3 place minced white of egg + .2 per cent 

 hydrochloric acid and pepsin. 



Treat No. 4 and No. 5 as No. 3. 



Place Nos. 1,2, and 3 in a water bath (or in a pail of 

 water over a radiator or register) where the tempera- 

 ture will stand at about 982° Fahrenheit for several 

 hours. 



Place No. 4 in the ice box or surround with ice for 

 three hours. Place No. 5 in boiling water for half an 

 hour, then place with Nos. 1, 2, and 3. 



Note all changes that have taken place in the differ- 

 ent tubes. 



A peptic gland, from 

 the stomach, very 

 much magnified. 

 A, central or chief 

 cells, which make 

 pepsin; B, border 

 cells, which make 

 acid. From Mil- 

 ler's Histology. 



