LESSON VII 

 THE DIGESTIVE JUICES 



SALIVA 



1. To a little saliva in a test-tube add acetic acid. Mucin is precipitated 

 in stringy flakes. 



2. Filter some fresh saliva to separate cells and mucus, and apply the 

 xanthoproteic or Millon's test to the nitrate; the presence of protein is 

 shown. 



3. Put some 0'5-per-cent. starch solution into two test-tubes. Add some 

 filtered saliva to one of them, and put both in the water-bath at 40 C. 

 After five minutes remove them and test both fluids with iodine and 

 Tronimer's test. The saliva will be found to have converted the starch into 

 dextrin and sugar (maltose). 



4. The presence of potassium sulphocyanide (KCNS) in saliva may be 

 shown by the refl. colour given by a drop of ferric chloride. This colour is 

 discharged by mercuric chloride. 



5. The reaction of saliva is alkaline to litmus paper. 



GASTRIC DIGESTION 



1. Half fill four test-tubes 



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

 per-ceiit. 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 protein 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 or syntonin is precipitated. 



(6) 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 (biuret 



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

 stomach. 



