PHYSIOLOGICAL CHEMISTRY. 



the reason why the stomach does not digest itself is, that during 

 life there is present in the mucous membrane of the stomach an 

 anti-enzyme (anti-pepsin) which has the property of inhibiting the 

 action of pepsin. A similar substance (anti-trypsin) is present in 

 the intestinal mucosa as well as in the tissues of various intestinal 

 worms. Some investigators are not inclined to accept the enzyme 

 nature of these inhibitory agents as proven. 



EXPERIMENTS ON ENZYMES AND ANTI-ENZYMES 

 A. Experiments on Enzymes. 1 



I. AMYLASES. 



1. Demonstration of Salivary Amylase. 2 To 25 c.c. of a one 

 per cent starch paste in a small beaker, add 5 drops of saliva and 

 stir thoroughly. At intervals of a minute remove a drop of the so- 

 lution to one of the depressions of a test-tablet and test by the iodine 

 test. 3 If the blue color with iodine stillr forms after five minutes, 

 add another five drops of saliva. The opalescence of the starch 

 solution should soon disappear, indicating the formation of soluble 

 starch (amidulin) which gives a blue color with iodine. This 

 body should soon be transformed into erythrodextrin which gives a 

 red color with iodine and this, in turn, should pass into achroodex- 

 trin which gives no color with iodine. This point is called the 

 achromic point. When this point is reached test by Fehling's test 4 

 to show the production of a reducing substance (maltose). A posi- 

 tive Fehling's test may be obtained while the solution still reacts red 

 with iodine inasmuch as some sugar is formed from the soluble 

 starch coincidently with the formation of the erythrodextrin. For 

 further discussion of the transformation of starch see p. 54. 



2. Demonstration of Pancreatic Amylase. 5 Proceed exactly 

 as indicated above in the Demonstration of Salivary Amylase ex- 

 cept that the saliva is replaced by 5 c.c. of pancreatic extract pre- 

 pared as described on p. 144. Pancreatic amylase transforms the 

 starch in a manner entirely analogous to the transformation result- 

 ing from the action of salivary amylase. 



1 If it is deemed advisable by the instructor to give all the practical work 

 upon enzymes at this point in the course, additional experiments will be found 

 in Chapters III, VI and VIII. 



2 For a discussion of this enzyme see p. 54. 



3 See p. 44. 

 * See p. 27. 



5 For a discussion of this enzyme see p. 142. 



