126 



PHYSIOLOGICAL CHEMISTRY. 



(b) Five c.c. of 0.4 per cent hydrochloric acid. 



(c) Five c.c. of pepsin-hydrochloric acid solution. 



(d) Two or three c.c. of pepsin solution and 2-3 c.c. of 0.5 per 

 cent sodium carbonate solution. 



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

 on the water-bath at 40 C. for one-half hour, carefully noting any 

 changes which occur. 1 Now combine the contents of tubes (a) 

 and (&) and see if any further change occurs after standing at 40 

 C. for 15-20 minutes. Explain the results obtained from these 

 five experiments. 



2. Influence of Different Temperatures. In each of four test- 

 tubes place 5 c.c. of pepsin-hydrochloric acid solution. Immerse 

 one tube in cold water from the faucet, keep a second tube at room 

 temperature and place a third on the water-bath at 40 C. Boil 

 the contents of the fourth tube 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? Explain this. 



3. The Most Favorable Acidity. Prepare three tubes as 

 follows : 



(a) Five c.c. of 0.2 per cent pepsin-hydrochloric acid solution. 



(b) Two or three c.c. of 0.2 per cent hydrochloric acid -f- i c.c. 

 of concentrated hydrochloric acid -f 5 c.c. of pepsin solution. 



(c) One c.c. of 0.2 per cent pepsin-hydrochloric acid solution 

 + 5 c.c. of water. 



Introduce a small piece of fibrin into each tube, keep them at 

 40 C., and note the progress of digestion. In which degree of 

 acidity does the fibrin digest the most rapidly? 



4. Differentiation Between Pepsin and Pepsinogen. Prepare 

 five tubes as follows : 



(a) Few drops of glycerol extract of pepsinogen + 2-3 c.c. of 

 water. 



(b) Few drops of glycerol extract of pepsinogen -f- 5 c.c. of 0.2 

 per cent hydrochloric acid. 



1 Digestion of fibrin in a pepsin-hydrochloric acid solution is indicated first by 

 a swelling of the protein due to the action of the acid, and later by a disintegra- 

 tion and dissolving of the fibrin due to the action of the pepsin-hydrochloric acid. 

 If uncertain at any time whether digestion has taken place, the solution under 

 examination may be filtered and the biuret test applied to the filtrate. A positive 

 reaction will signify the presence of acid metaprotein (acid albuminate), pro- 

 teoses (albumoses) or peptones, the presence of any one of which would indi- 

 cate that digestion has taken place. 



