68 PRACTICAL PHYSIOLOGY. [VIII. 



(3) perhaps debris of food, (4) possibly air-bubbles, and (5) fungi 

 especially various forms of bacteria (fig. 41). 



II. Physical and Chemical Characters (sp. gr. 1002-1006). 



(a.) Observe its appearance it is colourless and either trans- 

 parent or translucent and that when poured from one vessel tc 

 another it is glairy, and more or less sticky. On standing, it 

 separates into two layers ; the lower one is cloudy and turbid, and 

 contains in greatest amount the morphological constituents. 



(&.) Its reaction is alkaline to litmus paper. 



(c.) Add acetic acid = a precipitate of mucin not soluble in 

 excess. Filter. 



(d.) With the nitrate from (c.}, test for traces of proteids 

 (serum-albumin and globulin) with the xanthoproteic reaction and 

 Millon's test. 



(e.) To a few drops of saliva in a porcelain vessel add a few 

 drops of dilute acidulated ferric chloride = a red colouration due to 

 potassic sulpho-cyan ; de. The colour does not disappear on heat- 

 ing, or on the addition of an acid, but is discharged by mercuric 

 chloride. Meconic acid yields a similar colour, but it is not 

 discharged by mercuric chloride. The sulpho-cyanide is pre- 

 sent only in parotid saliva, and is generally present in mixed 

 saliva, 



(/.) Test a very dilute solution of potassic sulpho-cyanide to 

 compare with (e.). 



(g.) Gscheidlen's method. Dip filter paper in weak acidulated 

 (HC1) ferric chloride solution, and allow it to dry. Contact with a 

 drop of saliva gives a reddish stain. 



(//,) The salts are tested for in the usual way (see " Urine "). 

 Test for chlorides (HN0 3 and AgN0 3 ), carbonates (acetic acid), 

 and sulphates (barium chloride and nitric acid). 



(*'.) Nitrites are often present in saliva. Add a little of the saliva to starch 

 paste, containing a little sulphuric acid and iodide of potassium, when, if 

 nitrites be present, an intense blue colour is produced. 



(.;'. ) To diluted saliva add a few drops of sulphuric acid, and then meta- 

 diamido-benzol. Yellow colour indicates the presence of nitrites. This re- 

 action does not succeed in all cases. 



3. Digestive Action. 



Starch Solution. Place i gram of pure potato starch in a 

 mortar, add a few cc. of cold water, and mix well with the starch. 

 Add 200 cc. of boiling water, stirring all the while. Boil the 

 fluid in a flask for a few minutes. This gives .5 per cent, 

 solution. 



Action of Saliva on Starch (Ptyalin, a diastatic enzyme). 



(a.) Dilute the saliva with five volumes of water, and filter it. 



