CHAPTER VIII 

 GASTRIC DIGESTION 



Preparation of Artificial Gastric Juice 



Strip the mucous membrane from the stomach of a pig, and 

 cut into small pieces. Cut about % of the mucous membrane 

 into very small pieces, place in a small beaker and cover with 

 glycerine. Allow to stand at room temperature for 24 hours, 

 stirring occasionally. Decant or draw off with a pipette the 

 resulting glycerine solution of pepsinogen. This solution will 

 keep for a long time. Use it for the digestion experiments 

 in this chapter. To the remaining % of the gastric mucosa, 

 add 300 c.c. of 0.35% HC1 (3 c.c. of concentrated HC1 diluted 

 to 300 c.c.), a few c.c. of chloroform and set in the incubator at 

 40 for at least 48 hours, or longer if possible. The extracted 

 pepsin will digest the protein of the mucosa, and the mixture 

 may be studied for the products of peptic .digestion as described 

 below. 



I. Composition of Gastric Juice. 



a. Natural gastric juice contains small amounts of mucin 

 and other proteins. 



b. Inorganic salts, NaCl, earthy phosphates, etc. 



c. Acids, chiefly HC1. The acidity of the stomach contents 

 may be due to several factors, e. g., free HC1, organic acids, acid 

 combined with protein, and acid salts. The sum of these is 

 known as the total acidity. It may be determined by titrating 

 with N/10 NaOH, using phenolphthalein as indicator. Until 

 recently the individual factors which go to make up total acidity 

 have been estimated by the use of various indicators sensitive to 

 different concentrations of hydrogen-ions. These methods 

 have been shown to be subject to great inaccuracy. 



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