SALIVARY TESTS. 69 



167. Test for albuminous substances by the xan- 

 thoproteic reaction. 



168. Test for mucin by adding to the clear saliva 

 acetic acid drop by drop. The mucin separates in white, 

 stringy flakes. They may be washed with water and tested 

 by the mucin reactions. 



169. PREPARATION OF PTYALIN. Collect a large amount of 

 saliva and acidify with phosphoric acid. Then add milk of lime 

 until the liquid has a faint alkaline reaction. The phosphoric acid 

 is precipitated as calcium phosphate and carries the ptyalin down 

 with it. Filter and allow the water to drain off without washing. 

 Place the precipitate in a beaker and add not more water than 

 the original amount of the saliva. Stir it well and filter. This 

 removes the ptyalin from the calcium phosphate, and it goes into 

 the nitrate. Add to the nitrate an excess of alcohol. A white 

 precipitate will separate, which is ptyalin mixed with inorganic 

 salts. To free it from these, dissolve in a little water and pre- 

 cipitate with absolute alcohol. Repeat this operation if necessary. 

 Dry it over sulphuric acid. 



170. Test the aqueous solution of ptyalin. It is not precipi- 

 tated by nitric acid like albumin, nor does it give the xantho- 

 proteic reaction. It can be precipitated after a time by basic lead 

 acetate, the filtrate being without action on starch. 



171. Try the reaction of saliva to litmus and to 

 phenol-phthalein. Normally it is alkaline with the former 

 and neutral with the latter. Since alkaline salts affect 

 litmus while they do not change the color of phenol- 

 phthalein,, it is evident that here no free alkalies are pres- 

 ent, but that the reaction is due to alkaline salts. 



172. In a test-tube treat about 5 cubic centimeters 

 of a 1 per cent, solution of starch (made as in 6) with a 

 few drops of saliva and set it in water of body temperature. 

 From time to time remove a drop and test it with iodin 

 solution. Notice the change of color from the blue first ob- 



