1 68 ORGANIC AGRICULTURAL CHEMISTRY 



calcium phosphate which remains soluble when in the form of 

 calcium acid phosphate, but is precipitated as insoluble calcium 

 phosphate through the action of ammonia present in the breath. 

 The tartar also contains various other constituents in addition 

 to the calcium phosphate. 



Organic Substances. — In addition to the enzymes and in- 

 organic salts saliva also contains several organic substances, 

 viz. mucin, urea, an albumin and a globulin. The mucin is the 

 most important and is the constituent which gives to saliva its 

 mucilaginous character, acting as a lubricant in the passage of 

 the food down the esophagus. It is a glyco-protein (see p. 

 89). 



EXPERIMENT STUDY XXVII 

 Saliva and Salivary Digestion 



(i) Properties, (a) Collect 25-50 c.c. of saliva on a folded filter 

 paper in a funnel, and allow it to filter into a beaker or cylinder. 

 Note general properties, (b) With a urinometer, specific gravity 

 spindle or other form of hydrometer determine the specific gravity of 

 the filtered saliva, (c) Drop a piece of red litmus paper into the 

 saliva and allow to stand for some minutes. Note alkaline reaction 

 to litmus, (d) Make the Biuret and Millon's test for proteins (Ex- 

 periment XVIII, 4, a. c) with 5 c.c. of saliva. 



(2) Isolation and Test of Mucin, {a) Pour 50 c.c. of saliva into 250 

 c.c. of strong alcohol (95 %) in a tall beaker or cylinder. Allow to 

 stand a day or so. Carefully decant or siphon off all but a few cubic 

 centimeters of the supernatant liquid from the flocculent precipitate 

 of mucin. Slowly pour the remainder of the liquid containing the 

 mucin upon a small (7 cm.) filter paper in a funnel or filter through a 

 Witt plate with filter paper disk on top. Wash the mucin with two 

 or three small portions of alcohol and then a little ether. Remove 

 paper and scrape off the collected mucin with a knife blade, and place 

 it on the edge of a porous drying plate to dry. {b) After about 

 fifteen minutes take one half of the mucin and divide into three por- 

 tions. Make Millon's, Biuret and Xantho-proteic tests for proteins 

 (Experiment XVIII, 4, a. b. c). (c) Place the other half of the mucin 

 in beaker with 50 c.c, water. Add 5 c.c. of concentrated hydrochloric 



