SALIVA AND SALIVARY DIGESTION. 147 



tion with diastase. At a lower temperature with longer action 

 the conversion of the dextrin becomes more perfect. This 

 corresponds with the behavior of the pancreatic diastase which 

 is active through a longer period usually than is possible with 

 the saliva. 



BEHAVIOR OF THE DIASTASE. 



The question of the identity of the malt diastase with that 

 from saliva is still a disputed one ; while some writers describe 

 them as identical, others apparently find characteristic points 

 of difference. The behavior of saliva with various reagents 

 has been pretty thoroughly studied; stronger acids and alka- 

 lies have, of course, a destructive action, but experiments seem 

 to show that very weak acids favor rather than retard the 

 digestive power. When the acid strength is gradually in- 

 creased up to that of the gastric juice, the effect of the ptyalin 

 on starch paste grows weaker and finally becomes zero long 

 before the maximum acidity is reached. In the mouth the 

 action of the saliva is certainly largely mechanical, since the 

 time for any other action is entirely too short, but with the 

 passage of the food into the stomach it does not follow that 

 all diastatic digestion ceases because of the acid condition of 

 that organ. After the beginning of a meal some time is re- 

 quired for the commencement of hydrochloric acid secretion, 

 and a further time before enough has accumulated to seriously 

 interfere with the activity of the diastase. The effect of the 

 acid is dependent on its concentration, not on the gross amount 

 present. Up to a concentration of about o.oi per cent the acid 

 seems to have but little inhibiting action. Therefore while 

 this amount of free acid is accumulating we may suppose the 

 salivary digestion to go on in the stomach. Later, with in- 

 crease in acid, the ptyalin disappears, possibly through gastric 

 digestion. 



Many salts exert an influence on the rate of diastatic diges- 

 tion. Usually this is to retard the action, but sodium chloride 

 and other neutral salts in small amount have a beneficial effect. 

 With other substances the action is generally unfavorable. 



