146 PHYSIOLOGICAL CHEMISTRY. 



(d) 2-3 c.c. of neutral pancreatic extract + 2-3 c.c. of 0.2 per 

 cent hydrochloric acid. 



(<?) 2-3 c.c. of neutral pancreatic extract + 2-3 c.c. of 0.2 per 

 cent combined hydrochloric acid. 



(/) 2-3 c.c. of neutral pancreatic extract + 2-3 c.c. of 0.4 per 

 cent boric acid. 



(g) 2-3 c.c. of neutral pancreatic extract + 2 ~3 c - c - of -4 P er 

 cent acetic acid. 



Add a small piece of fibrin to the contents of each tube and 

 keep them at 40 C. noting the progress of digestion. In which 

 tube do we find the most satisfactory digestion, and why? How 

 do the indications of the digestion of fibrin by trypsin differ from 

 the indications of the digestion of fibrin by pepsin? 



2. The Most Favorable Temperature. (For this and the 

 following series of experiments under tryptic digestion use the 

 neutral extract plus an equal volume of 0.5 per cent sodium car- 

 bonate.) In each of four tubes place 5 c.c. of alkaline pancreatic 

 extract. Immerse one tube in cold water from the faucet, keep a 

 second at room temperature and place a third on the water-bath at 

 40 C. Boil the contents of the fourth for a few moments, then 

 cool and also keep it at 40 C. Into each tube introduce a small 

 piece of fibrin and note the progress of digestion. In which tube 

 does the most rapid digestion occur? What is the reason? 



3. Influence of Metallic Salts, etc. Prepare a series of tubes 

 and into each tube place 6 volumes of water, 3 volumes of alkaline 

 pancreatic extract and i volume of one of the chemicals listed in 

 Experiment 18 under Salivary Digestion, page 59. 



Introduce a small piece of fibrin into each of the tubes and keep 

 them at 40 C. for one-half hour. Shake the tubes frequently. 

 In which tubes do we get the least digestion ? 



4. Influence of Bile. Prepare five tubes as follows : 



(a) Five c.c. of pancreatic extract + l /2-i c.c. of bile. 



(b) Five c.c. of pancreatic extract + 1-2 c.c. of bile. 



(c) Five c.c. of pancreatic extract -f- 2-3 c.c. of bile. 



(d) Five c.c. of pancreatic extract -f- 5 c.c. of bile. 



(e) Five c.c. of pancreatic extract. 



Introduce into each tube a small piece of fibrin and keep them 

 at 40 C. Shake the tubes frequently and note the progress of 

 digestion. Does the presence of bile retard tryptic digestion? 

 How do these results agree with those obtained under gastric di- 

 gestion ? 



