126 DIGESTION AND ABSORPTION 



and the enzyme, pepsin. The meat known as tripe is the lining 

 of a cow's stomach and somewhat resembles the lining of the 

 human stomach. 



Problem. What is the effect of gastric juice on protein ? 



I. Prepare some very thin slices of hard-boiled white of egg. Put a slice 

 of this into each of four test tubes. Have the pieces alike in size. Add to the 

 four tubes the following liquids : 



A. Water, to tube number one. 



B. Water in which pepsin has been dissolved, to tube number two. 



C. Water and very dilute hydrochloric acid, to tube number three. 



D. Water, very dilute hydrochloric acid, and pepsin (artificial gastric 

 juice), to tube number four. Place all four test tubes and contents in a 

 warm place or in an incubator. 



II. Compare the appearance of the egg in the four tubes at the end of one, 

 two, four, eight, and twenty-four hours. What effect have the various con- 

 stituents of gastric juice on protein ? 



III. Give your explanation of the following : 



A. When people are suffering from indigestion, why are pepsin and 

 hydrochloric acid sometimes prescribed ? 



B. If there is too much hydrochloric acid in a person's stomach, why 

 is bicarbonate of soda sometimes prescribed ? 



C. Why is it unwise for a person to take artificial gastric juice or 

 bicarbonate of soda unless a doctor definitely prescribes it ? 



Problem. What is the effect of the size of protein food on the time 

 needed for digestion ? 



I. Place in a test tube some finely chopped white of egg. Put into an- 

 other test tube some larger pieces of white of egg, and into a third test tube, 

 some very large pieces of white of egg. Cover the egg white in each tube with 

 artificial gastric juice. 



II. Compare the appearance of the egg in the three tubes, hour by hour, 

 and note the results. 



III. What do you find to be the relation of the size of food to the time 

 needed for digestion ? Of what value is thorough mastication of food ? 



