50 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



pepsinogen. This latter substance shows considerable resist- 

 ance to reagents (dilute alkalies) which destroy pepsin. 

 Pepsinogen is itself inactive proteolytically, but seems to be 

 converted into active pepsin by the action of the HC1 of the 

 gastric juice. Pepsin belongs to the proteolytic enzymes, 

 converting proteins into proteoses, peptones, amino acids, 

 and diamines. The temperature of its optimum activity is 

 from 35-45 C. It is destroyed at 65 C. 



Pepsin is only active in acid solutions, and the amount of 

 acidity required for its maximum activity varies according to 

 the character of the acid employed and the form of protein 

 to be digested. Pepsin is easily destroyed by weak alkalies 

 (0.01 per cent), and less readily by strong acids (5-10 per 

 cent). 



The following set of experiments should prove these 

 facts: 



1. A glycerol extract of a pig's gastric mucosa contains 

 pepsinogen. 



2. A 0.2% HC1 extract of a pig's gastric mucosa contains 

 pepsin HCL 



3. A watery extract of a pig's gastric mucosa contains 

 pepsin. 



Make use of the above extracts numbered 1, 2, and 3 

 respectively, and in each test-tube add a piece of fibrin, 

 keeping all at 40 C. in the water-bath. 



(a) Fibrin + 5 c.c. of 0.2% HC1. 



(b) " +5 c.c. of solution 3. 



(c) " -f one drop of solution 1 + 5 c.c. of water. 



(d) " + 5 c.c. of solution 2. 



(e) " + one drop of solution 1 + 5 c.c. of 0.2% HC1. 

 (/) " + 5 c.c. of solution 2 (the latter having pre- 

 viously been heated to boiling and again cooled). 



(#) Fibrin + one drop of solution 1 (the latter having 



