I4 8 PHYSIOLOGICAL CHEMISTRY. 



Small amounts of protein matter, or preferably the syntonin 

 or acid albumins formed from the proteins by combination 

 with traces of hydrochloric acid, seem to increase slightly the 

 activity of the salivary diastase. This is a point of consider- 

 able importance in explaining possibly the continuation of the 

 ptyalin reaction in the stomach. Acid combined with protein 

 behaves as free acid toward certain indicators, while with other 

 indicators it does not show. Starch digestion with saliva in 

 a mixture containing protein and hydrochloric acid, as indi- 

 cated by dimethylaminoazobenzene, cannot continue, but if the 

 indication is merely by phenol-phthalein the ptyalin action may 

 still go on, since in this case the acid shown may possibly be 

 wholly or largely combined with protein substances. Recent 

 investigations have shown that under such conditions, which 

 are probably duplicated in the stomach, the digestion of starch 

 may go on at practically the normal rate, the hydrochloric acid 

 being rapidly combined with protein, and therefore compara- 

 tively inert with ptyalin. The alkalinity of human saliva is 

 usually referred to as due to the presence of sodium carbonate, 

 but soluble phosphates are present which may account for the 

 reaction as shown by certain indicators, especially by litmus. 

 With phenol-phthalein the reaction appears neutral ordinarily 

 or even slightly acid. With the latter substance as indicator 

 it is generally necessary to add a little alkali to secure neutral- 

 ity. With litmus as indicator the average alkalinity, expressed 

 in terms of Na 2 CO 3 , is 0.15 per cent. This reaction seems to 

 vary with the time of day and is strongest before breakfast. 

 Although carbon dioxide is present in saliva, it probably occurs 

 as bicarbonate rather than as carbonate, which would account 

 for the reactions noticed. 



Many soluble substances introduced into the blood in any 

 way soon appear in the saliva. This may be shown by an 

 experiment which illustrates also the rapidity of absorption. 



Ex. Swallow 2 grams of potassium iodide in a gelatin capsule. In this 

 manner the salt is gradually dissolved in the stomach without having come 

 in direct contact with the mouth. After a few minutes begin testing the 



