104 PHYSIOLOGY OF ALIMENTATION. 



Both acids and alkalies soon bring its activity to a stand- 

 still, even in very moderate concentrations. The influence 

 of acids upon amylolytic activity is of physiological impor- 

 tance, because the chewed food mixed with saliva passes 

 into the stomach. The concentration of the acid in the 

 stomach is sufficient to stop the activity of the amylase; 

 but, as will be remembered from what has been said before, 

 the amylase continues its action for some time, especially 

 in the cardiac end of the stomach, as the food which passes 

 into this viscus is not at once rendered acid by its secre- 

 tions. 



It has been shown by the work of CANNON that the saliva 

 does not act best in the concentration in which it is poured 

 out upon the food, but when diluted with about three times 

 its bulk of water. The explanation of this fact lies no 

 doubt in the dilution of the products of amylolytic activity, 

 for in a concentrated solution the point at which the reac- 

 tion comes to a standstill is reached sooner than in a more 

 dilute one. In fact, most fermentation mixtures which 

 have come to a standstill will go on further if only water 

 is added. The use of water with meals, after thorough 

 mastication of the food, is therefore not only not harmful, 

 but useful. Dilution of the stomach contents hastens the 

 activities f the enzymes here also. The presence of water 

 in the stomach, moreover, increases the secretion of gastric 

 juice and hastens absorption. The evil consequences of the 

 consumption of water with meals lie in its use before masti- 

 cation of the food, thus preventing thorough insalivation and 

 the good effects of this process upon the food; and in the use 

 of too cold water, whereby the reaction velocity of all fer- 

 mentative changes is markedly decreased. 



2. Maltase (glucase) is an enzyme the characteristic activ- 

 ity of which lies in its power of splitting maltose into two 

 molecules of dextrose. It is able to act also upon starches 

 and dextrins, but only exceedingly weakly when compared 

 with amylase, the ultimate product from these substances 



