144 The Inorganic Components of Saliva 



occurs in the salivary ducts along the osmotic gradient that is 

 present. This suggestion was based on the finding that a number 

 of non-electrolytes are concentrated in the saliva above the plasma 

 levels at low rates of saliva secretion. This can readily be under- 

 stood if water reabsorption from the saliva occurred at a site in the 

 ducts more distal to those across which non-electrolyte movement 

 can occur. Direct evidence for this is available in the case of urea. 



pH AND BICARBONATE CONCENTRATION 



The hydrion concentration in saliva can only be determined if 

 adequate means are taken to prevent loss of dissolved carbon 

 dioxide and may then be determined either directly or from 

 measurement of the bicarbonate concentration and the pC0 2 . 

 Schmidt-Nielsen (19460) has described a satisfactory method with 

 a microquinhydrone electrode and analysed the sources of error 

 in the method. He found the pH of the resting parotid saliva in 

 40 adults to average 5-81 (range 5-45-6-06) and the submaxillary 

 saliva a little higher at 6-39 (range 6-02-7-14); on activation the 

 pH of the parotid saliva increased by up to 2 units, the maximum 

 pH recorded being 7-80 (Schmidt-Nielsen, 19466). Rauch (1956) 

 obtained similar values (i.e. 5-1-6-3 for parotid and 5-9-7-3 for 

 submaxillary), as did Chauncey, Lisanti and Winer (1958). Chaun- 

 cey and Weiss (1958) showed that acetazoleamide was without 

 effect on the pH. Sand (1949) measured the pC0 2 of human sub- 

 maxillary and sublingual saliva and found it to be 53-60 mm Hg 

 and practically independent of the rate of secretion. This means 

 that the pH of the saliva can be predicted from the bicarbonate 

 concentration. Sand found that the opalescence that often develops 

 when saliva stands in the air was due to the formation of Ca 3 (P0 4 ) 2 

 when the pC0 2 was less than 20 mm Hg. Sand also found that the 

 pH of saliva increased with increasing flow of the saliva. This 

 has been confirmed in human parotid saliva (Hildes and Ferguson, 

 1955; Anderson, 1949). Yoshimura, Iwasaki, Nishikawa and 

 Matsumoto (1959) have found that sublingual saliva in the dog 

 has a fixed pH of about 7-2. Yoshimura, Takaoka and Mori (1954) 

 have found that the pC0 2 of saliva is increased when the pC0 2 

 of the plasma is increased. As pointed out below, since the bicar- 

 bonate concentration of the saliva is also affected by changes in the 

 arterial pC0 2 , the saliva pH is little affected by respiratory acidosis 

 and alkalosis. 



