68 THE SALIVA. 



tal of tartaric acid or filling it with the vapor of ether or 

 acetic acid ; or by electrical excitation. In collecting saliva 

 for testing it should be accomplished without trying to 

 hasten its flow by suction with the tongue as this increases 

 the amount of secretion from the mucous membrane and 

 so dilutes the secretion of the salivary glands. 



The composition of the saliva is changed by certain 

 pathological conditions. The amount is diminished in all 

 febrile conditions^ also in diabetes and often in nephritis. 

 It is increased by the action of some medicinal substances, 

 like the mercury compounds, pilocarpine, and others ; also 

 by anything which causes irritation or inflammation of the 

 glands. Urea has been found in it abundantly during 

 nephritis. The reaction becomes acid in fevers and in 

 diabetes, and this sometimes happens also after long-con- 

 tinued talking. 



163. Collect for examination some saliva by letting 

 it flow into the mouth without swallowing. Excite the 

 flow by chewing a piece of soft paraffin. Notice the indi- 

 cation of mucin in the viscidity, as well as the lasting foam 

 after beating it with a glass rod. 



164. Let a portion stand exposed to the air, and 

 notice the separation of calcium carbonate as a white film 

 or turbidity. 



165. Test a portion for potassium sulphocyanate by 

 adding to it a very dilute solution of ferric chlorid. A 

 red color indicates the sulphocyanate. This is immediately 

 decolorized by the addition of a few drops of mercuric 

 chlorid solution. 



166. Test for nitrites with a few drops of a starch 

 solution acidified with a little dilute sulphuric acid and 

 containing a small amount of potassium iodid. A nitrite 

 immediately gives a blue color. 



