1 90 PHYSIOLOGICAL CHEMISTRY 



phane (see page 77. Also see glycyl-tryptophane reaction in chapter on Intes- 

 tinal Digestion). To another 5 c.c. add 10 drops of concentrated sulphuric acid 

 and 10 c.c. of a 10 per cent solution of mercuric sulphate in 5 per cent sulphuric 

 acid. Shake the tube and allow to stand five minutes. A yellow precipitate of a 

 mercury compound of tryptophane forms. 1 Concentrate 2 the remainder of the 

 three-fourths portion to a thin syrup and make the separation of leucine and tyro- 

 sine according to the directions given on page 85. 



GENERAL EXPERIMENTS ON PANCREATIC DIGESTION 



EXPERIMENTS ON TRYPSIN 3 



1. The Most Favorable Reaction for Tryptic Digestion. Prepare seven tubes 

 as follows: 



(a) 2-3 c.c. of neutral pancreatic extract +2-3 c.c. of water. 



(b) 2-3 c.c. of neutral pancreatic extract+2-3 c.c. of i per cent sodium car- 

 bonate. 



(c) 2-3 c.c. of neutral pancreatic extract+2-3 c.c. of 0.5 per cent sodium 

 carbonate. 



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

 chloric acid. 



(e) 2-3 c.c. of neutral pancreatic extract+2-3 c.c. of 0.2 per cent combined 

 hydrochloric acid. 



(f) 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 0.4 per cent acetic acid. 

 Add a small piece of fibrin 4 to the contents of each tube and keep them at 4OC. 



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 carbonate.) 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 in the incubator or water-bath at 

 4OC. Boil the contents of the fourth for a few moments, then cool and also keep 

 it at 40C. 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 Bile. Prepare three tubes as follows : 



(a) 5 c.c. of pancreatic extract +1/2-1 c.c. of bile. 



(b) 5 c.c. of pancreatic extract +5 c.c. of bile. 



1 It has been claimed that a similar yellow precipitate forms in the presence of tyrosine, 

 cystine and polypep tides. For quantitative estimation of tryptophane see Homer: Jour. 

 Biol. Chem., 22, 369, 1915. 



2 If the solution is alkaline in reaction, while it is being concentrated, the amino acids 

 will be broken down and ammonia will be liberated. 



3 For these experiments as well as for those on the other pancreatic enzymes commer- 

 cial preparations of trypsin and pancreatin may be employed. 



4 Congo red fibrin may be used in this and the following tests on tryptic digestion. If 

 used the experiments should be made at room temperature. For preparation of this 

 fibrin see Chapter I. 



