48 PHYSIOLOGY FOR DENTAL STUDENTS. 



well as the saliva. In contrast to cyanides it is non-poisonous, so 

 that it represents the inocuous form into which these substances 

 are converted. 



The chemical test used for its detection is the red color which 

 it gives with a solution of ferric chloride (FeCl 3 ). Sometimes, 

 however, the reaction is not very definite, in which case the 

 method of Bunting should be employed. This is performed as 

 follows : Slowly evaporate 5 c. c. of saliva in a watch glass and 

 while stirring with a glass rod add a few drops of a 26 per cent 

 solution of FeCl 3 . Pour about 5 c. c. of a mixture of 5 parts 

 amyl alcohol and 2 parts ether over the residue, and after stir- 

 ring decant into a test tube. If sulphocyanide is present, the 

 alcohol-ether will become red. Benzoate and aceto acetic acid 

 may give a similar reaction, but most of the other substances 

 which might interfere witii the test, as when it is done by merely 

 adding FeCl 3 to saliva, are eliminated by Bunting's method. 



All this care and interest in the testing for KCNS has arisen 

 because of the supposition that the amount of this substance in 

 saliva might have some relationship to caries of the teeth. It 

 was suggested that it might confer on the saliva somewhat of an 

 antiseptic action and thus destroy the bacteria that are the cause 

 of caries. Careful work by Bunting, by Gies and others has. 

 however, shown that this hypothesis is untenable. 



Inorganic Constituents. Two important questions arise in 

 connection with these, viz: (1) their relationship to the reaction 

 of the saliva; (2) the conditions which control the precipitation 

 of calcium carbonate and phosphate and the deposition of the 

 precipitate on the teeth in the form of tartar. 



THE REACTION OF THE SALIVA. Tested with litmus paper sa- 

 liva is more or less alkaline and it is distinctly so towards lac- 

 moid and Congo red, but it is acid when tested with phenolph- 

 thalein. It is thus said to be amphoteric, like blood and urine 

 Difficulty in deciding as to the reaction of saliva is partly due 

 to the fact that it changes on standing because carbon-dioxide 

 (CO 2 ) is dissipated, thus making it more alkaline. To succeed 

 in determining the reaction of saliva, we must therefore under- 

 stand to what its amphoteric behavior is due and we must con- 



