52 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



LESSON VI 

 PEPTIC DIGESTION 



1. Half fill four test-tubes — 



A with water. B with 0-2-per-cent. hydrochloric acid. C with 0"2- 

 per-cent. hydrochloric acid. D with solution of white of egg (1 to 

 10 of water). 



2. To A add a few drops of glycerin extract of stomach ' (this contains 

 pepsin) and a piece of a solid proteid like fibrin. 



To B also add pepsin solution and a piece of fibrin. 

 To C add only a piece of fibrin. 



To D add a few drops of pepsin solution and fill up the tube with 0"2-per- 

 cent. hydrochloric acid. 



3. Put the tubes into the water-bath at 40° C, and observe them care- 

 fully. 



In A the fibrin remains unaltered. 



In B it becomes swollen, and gradually dissolves. 



In C it becomes swollen, but does not dissolve. 



4. After half an hour examine the solution in test-tube B. 



(a) Colour some of the liquid with litmus and neutralise with dilute 

 alkali. Acid-albumin, syntonin, or parapeptone is precipitated. 



(b) Take another test-tube, and put into it a drop of 1-per-cent. solution of 

 copper sulphate ; empty it out so that the merest trace of copper sulphate 

 remains adherent to the wall of the tube ; then add the solution from test- 

 tube B and a few drops of strong caustic potash. A pink colour (biiuret re- 

 action) is produced. This should be carefully compared with the violet tint 

 given by unaltered albumin. 



(e) To a third portion of the fluid in test-tube B add a drop of nitric acid ; 

 albumoses or propeptones are precipitated. This precipitate dissolves on 

 heating and reappears on cooling. 



5. Repeat these three tests with the digested white of egg in test-tube D. 



6. Examine an artificial gastric digestion which has been kept a week. 

 Note the absence of putrefactive odour ; in this it contrasts very forcibly 

 with an artificial pancreatic digestion under the same circumstances. 



THE SECRETION OF GASTRIC JUICE 



The juice secreted by the glands in the mucous membrane of the 

 stomach varies in composition in the different regions, but the mixed 

 gastric juice, as it may be termed, is a solution of a proteolytic fer- 

 ment called pepsin in a saline solution, which also contains a littlo 

 free hydrochloric acid. 



' Benger's liquor pepticus may be used instead of the glycerin extract of 

 stomach. 



