CHEMISTRY OF SALIVA. 



51 



that the neutralizing power of saliva, collected without any ef- 

 fort or artificial stimulation of the mouth (resting saliva), is 

 very distinctly less than that of saliva collected whilst chewing 

 on a piece of paraffin (activated saliva), and that this difference 

 becomes -very much Jess in those with carious teeth. Marshall 

 has suggested that we should express the ratio of the neutraliz- 

 ing power of resting saliva to that of activated saliva as a per- 

 centage ratio, which he calls the salivary factor. In persons im- 

 mune from caries this factor amounted to 43-80; in those with 

 caries it varied from 80-132. The following examples will illus- 

 trate these points : 



NORMAL RESTING SALIVA 



ACTIVATED SALIVA 



If these interesting observations should prove to be confirmed 

 by other observers, it will supply us with a comparatively simple 

 method for solving what has hitherto been a most puzzling ques- 

 tion and which has prompted several observers, particularly 

 Bunting and Price, to employ the very delicate physico-chemical 

 methods of the concentration cell (p. 31) and electrical conduc- 

 tivity to its elucidation. 



Before leaving the subject of the relationship between the 

 character of the saliva and the occurrence of dental caries, it 

 may be well to point out that other factors besides the neutral- 

 izing power of the saliva must be taken into consideration, name- 

 ly, its amount and the presence of phosphates. A large and free 

 flow of saliva, besides mechanically cleansing the teeth, will offer 

 more neutralizing fluid. An excess of phosphates, on the other 

 hand, will encourage fermentation of any carbohydrate which 

 may be adherent to the teeth and, by forming acids, thus tend to 

 erode the teeth and predispose to caries. 



