ELEMENTARY CHEMICAL PHYSIOLOGY 227 



examine under the microscope : two kinds of cells will be seen, 

 viz. (1) large, flat, squamous cells, which have been desquamated 

 from the surface of the stratified epithelium of the mouth ; (2) 

 small round cells like leucocytes, which come either from the 

 salivary glands or from the tonsils. 



EXPERIMENT III. Place some saliva in a test tube and dilute 

 it with an equal quantity of water ; now add a few drops of 10 per 

 cent, acetic acid, when a stringy precipitate of mucus will form. 

 Filter off this precipitate, and note that the filtrate is watery, 

 showing that the viscid character of saliva is due to the mucus 

 which it maintains. To the filtrate add a few drops of Millon's 

 reagent and boil. The result shows the presence of protein. 



EXPERIMENT IV. Add to some saliva in a test tube a drop of 

 a weak solution of ferric chloride (Liq. Ferri Perchlor. B.P.) and 

 a drop of hydrochloric acid. A red colour is sometimes produced. 

 This is due to the production of ferric sulphocyanide by interaction 

 between the ferric chloride and a sulphocyanide which is contained 

 in saliva. The red colour is discharged by adding a few drops of 

 a solution of mercuric chloride (1-1,000). A more sensitive way of 

 performing this test is to place a drop of saliva at one end of a piece 

 of filter paper, and then to allow a drop of ferric chloride solution 

 (acidified with HC1) to spread to the edge of the saliva drop ; a deep 

 red stain will result where the two moistened areas meet. 



EXPERIMENT V. If some saliva be allowed to stand for an hour 

 or so, it becomes milky or a thin surface film forms on it. This is 

 due to the precipitation of calcium carbonate, which exists in fresh 

 saliva in a soluble state as calcium bicarbonate. On standing 

 exposed to the air, however, carbonic acid gas is given off, in con- 

 sequence of which the bicarbonate changes into carbonate, which 

 is insoluble. A similar precipitation of calcium carbonate, carrying 

 with it a certain amount of calcium phosphate, sometimes occurs 

 in the ducts of the glands and leads to the formation of calculi, 

 or it may form on the teeth, where it leads to the formation of 

 tartar. 



II. To Study the Action of the Ferment Ptyalin. 



EXPERIMENT VI. Place a few cubic centimetres of a 0-5 per cent, 

 solution of starch in two test tubes, a and 6. To 6 add about an 

 equal amount of saliva, and place both a and b in the water-bath 

 at 37-40. Note that in a very few minutes the solution in b 

 loses its opalescence and becomes clear. By means of glass rods 

 transfer drops from each solution, about once a minute, to a white 

 slab or dry evaporating dish, and add to each drop a little iodine 

 solution. In the drops from the test tube b the blue colour 

 becomes at first purplish and then reddish brown, and ultimately 

 disappears. When this stage has been reached, apply Trommer's or 

 Fehling's test to the contents of the test tube, and note that reduc- 

 tion occurs. In the case of a the blue colour persists throughout 

 and reduction of cupric salts does not occur. 



What has occurred in b is that the ptyalin has hydrolysed the 



