80 PHYSIOLOGY FOR THE LABORATORY. 



Experiment : 



1. To the first test-tube add 10 c.c. of water. 



2. To the second test-tube add 10 c.c. of dilute 



hydrochloric acid. 



3. To the third test-tube add 10 c.c. of pepsin and 



water. 



4. To the fourth test-tube add 10 c.c. of pepsin 



and dilute hydrochloric acid. 



5. Place all the test-tubes in the warm bath and 



notice the results at the end of one or two 

 hours. 



IV. THE ACTION OF GASTRIC JUICE ON MILK. 



Materials. 10 c.c. of milk. 10 c.c. of water. A few grains of 

 pepsin. Rennet. 



Apparatus. Test-tubes. Warm water-bath. 



When the milk reaches the stomach it is first acted 

 upon by the rennin and then by the pepsin and hydro- 

 chloric acid. 



Experiment : 



1. The action of the rennin. (Rennin is the essen- 



tial element of rennet, which is obtained from 

 the fourth stomach of the calf.) Add 4 or 5 

 drops of rennet to the milk in a test-tube, 

 and allow it to stand a few minutes in the 

 warm water-bath. What is the curd and the 

 whey ? What is the action of rennin on milk ? 



2. The action of pepsin. Mix the curdled milk, 



the pepsin, and water in a test-tube and place 

 it in the warm water-bath. . Look at it every 

 fifteen minutes. What takes place ? 



