122 PHYSIOLOGICAL CHEMISTRY. 



juice is of normal acidity, but evinces its action principally at such 

 times as a gastric juice of low acidity is secreted either from 

 physiological or pathological cause. The digestion of fat in the 

 stomach is, however, at most, of but slight importance as com- 

 pared with the digestion of fat in the intestine through the action of 

 the lipase of the pancreatic juice (see page 143). 



PREPARATION OF AN ARTIFICIAL GASTRIC JUICE. 



Dissect the mucous membrane of a pig's stomach from the mus- 

 cular portion and discard the latter. Divide the mucous membrane 

 into two parts (4/5 and 1/5). Cut up the larger portion, place 

 it in a large-sized beaker with 0.4 per cent hydrochloric acid and 

 keep at 38-4O C. for at least 24 hours. Filter off the residue, 

 consisting principally of nuclein and anti-albumid, and use the 

 filtrate as an artificial gastric juice. This filtrate contains pepsin, 

 rennin and the products of the digestion of the stomach tissue, 

 i. e.j acid metaprotein (acid albuminate), proteoses, peptones, etc. 



PREPARATION OF A GLYCEROL EXTRACT OF PIG'S STOMACH. 



Take the one-fifth portion of the mucous membrane of the pig's 

 stomach not used in the preparation of the artificial gastric juice, 

 cut it up very finely, place it in a small-sized beaker and cover the 

 membrane with glycerol. Stir frequently and allow to stand at 

 room temperature for at least 24 hours. The glycerol will extract 

 the pepsinogen. Separate, with a pipette or by other means, the 

 glycerol from the pieces of mucous membrane and use the glycerol 

 extract as required in the later experiments. 



PRODUCTS OF GASTRIC DIGESTION. 



Into the artificial gastric juice, prepared as above described, 

 place the protein material (fibrin, coagulated egg-white, or lean 

 beef) provided for you by the instructor, add 0.4 per cent hydro- 

 chloric acid as suggested by the instructor and keep the digestion 

 mixture at 40 C. for 2 to 3 days. Stir frequently and keep free 

 hydrochloric acid present in the solution (for tests for free hydro- 

 chloric acid see p. 123). 



The original protein has been digested and the solution now con- 

 tains the products of peptic proteolysis, i. e. } acid metaprotein (acid 

 albuminate), proteoses, peptones, etc. The insoluble residue may 

 include nuclein and anti-albumid. Filter the digestive mixture and 



