BY DR. LAUDER BRUNTON. 459 



be added, then sodium phosphate. Potassium Sulphocyanide. 

 This is generally, though not invariably, present in mixed 

 saliva. It is derived from the saliva secreted by the parotid 

 gland, and is not contained in that of the submaxillary gland. 

 To show its presence, add a drop of solution of perchloride of 

 iron, so veiy dilute as to be almost colorless, to a little saliva 

 in a porcelain crucible or capsule, and stir it. A reddish color 

 is developed, which remains unchanged after the addition of 

 hydrochloric acid, but is at once removed by a solution of cor- 

 rosive sublimate. Perchloride of iron gives a similar color 

 with acetic acid and with meconic acid, but the color produced 

 in the former case is destroyed by hydrochloric acid and in 

 the latter by mercuric chloride. When undiluted perchloride 

 of iron is used, the color is deep red, and may be shown to 

 persons at a little distance. If the test does not at first suc- 

 ceed, the saliva should be evaporated to one-third of its bulk, 

 and the test then applied. 



To determine the percentage of inorganic salts, the dry resi- 

 due must be incinerated (see 214), weighed, and calculated, 

 as in 74. 



* 76. Organic Constituents. These are albumin, mucin, 

 ptyalin. Albumin. If saliva is strongly acidified with nitric 

 acid, it becomes turbid, but no precipitate is formed. On then 

 boiling it becomes clearer, and the color changes to yellow ; 

 the addition of ammonia changes the 3 r ellow to orange-red. 

 If to another portion a mixture of acetic acid and potassium 

 ferrocyanide is added, a white precipitate is produced. Saliva 

 contains two albuminous bodies albumin proper dissolved in 

 salts, and globulin. Globulin is precipitated from dilute solu- 

 tions by CO 2 , ordinary albumin is not. To separate them, a 

 stream of carbonic acid gas must be passed through saliva, di- 

 luted with a large quantity of water, for some time. A very 

 fine flocculent precipitate is formed, which tends to disappear 

 when the turbid liquid is agitated with air. After the precipi- 

 tate has settled, the liquid may be decanted off with a syphon, 

 and. if needful, filtered ; it can then be proved to contain albu- 

 min by the addition of acetic acid and ferrocyanide of potas- 

 sium. This process requires considerable care. Mucin. To 

 this bod}' is due the stickiness and tenacity of saliva. If acetic 

 acid is gradually added to saliva while it is stirred with a 

 glass rod, it becomes more and more tenacious, and finally the 

 mucin separates in white stringy flakes ; these must be washed 

 with water and acetic acid, and tested b} T the reactions given 

 in 45. 



** 77. Action of Saliva on Starch Paste. Saliva con- 

 verts starch into sugar. To show this, prepare some thin 

 mucilage by rubbing up a little starch with cold water into a 

 smooth paste and pouring a large quantity of boiling water 



