SECRETION OF GASTRIC JUICE 



127 



Problem. What animal proteins are digested most quickly and most 

 thoroughly f 



I. Put into separate tubes equal-sized, thin slices of the following proteins : 



A. Well-boiled beef. D. Roast pork. 



B. Raw beef. E. Roast lamb. 



C. Roast beef. F. Fried fish. 



Pour an equal amount of the artificial gastric juice into each tube. Place 

 the tubes in a warm place. 



II. Compare at regular intervals the amounts of protein in each tube. 



III. State your conclusion from your observations. 



opening into 

 the storitcutK* 



large, < 



on the inner 



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Secretion of gastric juice. The secretion of gastric juice is 

 continuous. Even when one is not eating there is a small amount 

 of secretion, but during 

 the act of eating and 

 throughout the entire 

 period of digestion, the 

 rate of secretion is greatly 

 increased. This rate is 

 regulated by several fac- 

 tors : (1) Psychical stimu- 

 lations are brought about 

 by the sensations of eat- 

 ing. The taste and odor 

 of food stimulate the be- 

 ginnings or receptors of 

 certain sensory nerves sit- 

 uated in the mouth and 

 nose. This stimulation 

 results in activating the gastric glands. It has been demon- 

 strated, experimentally, that as soon as a dog tastes, smells, or 

 sees food, the flow of gastric juice increases. A psychic stimu- 

 lation results in a copious flow of gastric juice. Such a stimula- 

 tion is always brought about when one eats appetizing food. 



In a gastric gland certain cells secrete pepsin, while 

 certain others secrete hydrochloric acid. With water, 

 these substances are the main constituents of gastric 

 juice which is emptied from the gland into the stomach. 



