144 PHYSIOLOGICAL CHEMISTRY 



gastric juice .of low acidity is secreted either from physiological or patho- 

 logical cause. The digestion of fat in the stomach is, however, at 

 most, of but slight importance as compared with the digestion of fat in 

 the intestine through the action of the lipase of the pancreatic juice 

 (see page 188). 



Boldyreff 1 has shown trypsin to be present in stomach contents, due 

 to regurgitation of intestinal contents through the pylorus. This claim 

 has been verified by others 2 (see Chapter VIII on Gastric Analysis) . 



PREPARATION OF AN ARTIFICIAL GASTRIC JUICE 



Dissect the mucous membrane of a pig's stomach from the muscular 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 38-4oC. for at least 24 hours. Filter off the 

 residue, consisting of nuclein and other substances, and use the filtrate as 

 an artificial gastric juice. This filtrate contains pepsin, rennin, and the prod- 

 ucts of the digestion of the stomach tissue, i.e., acid metaprotein (acid albu- 

 minate), 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 hydrochloric acid as suggested by the instructor and 

 keep the digestion mixture at 4OC. for two to three days. Stir frequently and 

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

 chloric acid see page 152). 



The original protein has been digested and the solution now contains the 

 products of peptic proteolysis, i.e., acid metaprotein (acid albuminate), proteoses, 

 peptones, etc. The insoluble residue may include nuclein and other substances. 

 Filter the digestion mixture and after testing for free hydrochloric acid neutralize 

 the filtrate with potassium hydroxide solution. If any of the acid metaprotein 

 (acid albuminate) is still untransformed into proteoses it will precipitate upon 

 neutralization. If any precipitate forms heat the mixture to boiling, and filter. 

 If no precipitate forms proceed without filtering. 



1 Boldyreff: Quart. Jour. Exper. PhysioL, 8, i, 1914. 



2 Spencer, Meyer, Rehfuss and Hawk: Am. Jour. Physiol, 39, 459, 1916. 



