146 PHYSIOLOGICAL CHEMISTRY 



I 



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 + 5 c.c. of 0.2 per cent hydro- 

 chloric acid. 



(c) Few drops of glycerol extract of pepsinogen -f 5 c.c. of 0.5 per cent sodium 

 carbonate. 



(d) Two or 3 c.c. of pepsin solution + 2-3 c.c. of i per cent sodium carbonate. 



(e) Few drops of glycerol extract of pepsinogen + 5 c.c. of i per cent sodium 

 carbonate. 



Add a small piece of fibrin to the contents of each tube, keep the five tubes at 

 4OC. for one-half hour and observe any changes which may have occurred. To 

 (a) add an equal volume of 0.4 per cent hydrochloric acid, neutralize (c), (d) and 

 (e) with hydrochloric acid and add an equal volume of 0.4 per cent hydrochloric 

 acid. Place these tubes at 4OC. again and note any further changes which may 

 occur. What contrast do we find in the results from the last three tubes? 

 On the basis of these tests what is the relative resistance of pepsin and pepsinogen 

 to alkalis? 



5. Comparative Digestive Power of Pepsin with Different Acids. Prepare a 

 series of tubes each containing a N/io solution of one of the following acids: 

 hydrochloric, sulphuric, nitric, combined hydrochloric, acetic, lactic and oxalic. 

 To each acid add a few drops of the glycerol extract of pig's stomach and a small 

 piece of fibrin. Shake well, place at 4OC., and note the progress of digestion. 

 In which tubes does the most rapid digestion occur? 



6. Influence of Metallic Salts, etc. Prepare a series of tubes and into each 

 tube introduce 4 c.c. of pepsin-hydrochloric acid solution and 0.5 c.c. of one of the 

 chemicals listed in Experiment 19 under Salivary Digestion, page 60. Introduce a 

 small piece of fibrin into each of the tubes and keep them at 40 C. for one-half hour. 

 Note the variations in the progress of digestion. Where has the least rapid diges- 

 tion occurred? 



7. Sahli's Desmoid Reaction. This is a method for testing gastric function 

 without using the stomach tube. The underlying principle of the test is the fact 

 that raw catgut may be digested in gastric juice but is entirely indigestible in 

 pancreatic juice. The test is made as follows : A methylene-blue pill is intro- 

 duced into a small rubber bag and the mouth of the bag subsequently tied with 

 catgut. l The small bag is then ingested immediately after the mid-day meal and 

 the urine examined 5, 7, 9 and 18-20 hours later for methylene blue. If methyl- 

 ene blue is present in appreciable quantity, it will impart to the urine a greenish- 

 blue color. If not present in sufficient amount to impart this color the urine should 

 be boiled with one-fifth its volume of glacial acetic acid, whereupon a greenish- 

 blue color results if the chromogen of methylene blue is present. This contin- 

 gency seldom arises, however, inasmuch as in most cases of uncolored urine it will 



1 About 0.05 gram of methylene blue is mixed with sufficient ext. glycyrrhiza to form 

 a pill about 3-4 mm. in diameter. The pill is then placed in the center of a square piece 

 of thin rubber dam and a little bag-like receptacle constructed by a twisting movement. 

 The neck of the bag is then closed by wrapping three turns of catgut about it. The 

 most satisfactory catgut to use is number oo raw catgut which has previously been soaked 

 in water until soft. When ready for use the bag should sink instantly when placed in 

 water and be water-tight. 



