78 PHYSIOLOGY FOR THE LABORATORY. 



Experiment : 



1. Make a dilute starch paste of pure potato starch 



and boil for a few minutes. One grain of 

 starch to 200 c.c. of water is sufficient. 



2. Dilute 5 c.c. of saliva with 25 c.c. of water. 



3. Place one of the following solutions in each of 



three test-tubes : 



(1) 20 c.c. of starch paste. 



(2) 20 c.c. of diluted saliva. 



(3) 5 c.c. of saliva and 15 c.c. of starch 



paste. 



4. Place in the warm bath for ten minutes and then 



test each for maltose. What is the effect of 

 saliva on starch ? Why was the mixture kept 

 at a temperature of 42 C. ? 



B. The Gastric Juice. 

 I. THE PREPARATION OF ARTIFICIAL GASTRIC JUICE. 



Materials. | a gram of pepsin. 2 c.c. of strong hydrochloric 



acid. 50 c.c. of water. 



Apparatus. A small beaker. A warm water-bath and ther- 

 mometer. 



The essential constituents of gastric juice are hydrochloric 

 acid, pepsin, and rennin. As far as we know, the action of 

 rennin is confined to th^ curdling of milk, so that a solution 

 of pepsin, slightly acidulated with hydrochloric acid, rep- 

 resents the action of the normal gastric juice on proteids. 



Experiment : 



Mix the water, the acid, and the pepsin in the beaker 

 and place this in a warm water-bath. Insert the ther- 



