2-18 A. I. RIXGEK AND EMIL J. BAUMANX 



nose and glucose. Phosphoric acid is usually associated with the gums, 

 as with many other polysaccharides, and it is most difficult if not impos- 

 sible to separate them. This suggests that sugar phophate may be pres- 

 ent in the polysaccharide molecule. Phosphoric acid sugar compounds 

 plav a great role in biochemical phenomena. 



Digestion of Carbohydrates 



The carbohydrates that play a role in human metabolism are the poly- 

 saccharides, starches, glycogen and cellulose, and the disaccharides, suc- 

 rose, lactose and maltose. During the process of digestion, the higher 

 carbohydrates are converted into monosaocha rides, by processes of hydro- 

 Ivsis. 



v 



Salivary Digestion, The first enzyme that acts upon carbohydrates 

 is encountered in the salivary secretion and is known under the names of 

 amylolytic ferment, diastase and ptyalin. It is a ferment that is suscep- 

 tible to changes in temperature. At C. its activity is entirely suspended, 

 whereas at body temperature it shows its optimum activity. If the tem- 

 perature is raised above that, its activity diminishes until it reaches 65 to 

 70 C., when it is completely destroyed. 



It is also highly sensitive to the hydrogen ion concentration, showing 



greatest activity in an acid concentration of , An acid solution of 



1ST 



inhibits the action .of the diastase completely, as will also a strongly 



fl 



100 



alkaline reaction. 



Salts, especially phosphates, seem necessary for ptyalin digestion for, 

 when saliva is dialyzed, it loses much of its amylolytic powers. These 

 may be restored by the addition of a little phosphate. It is quite pos- 

 sible that a carbohydrate-phosphate intermediary product of digestion is 

 formed similar to the hexose-phosphate that Harden and Young found 

 to be essential in fermentation. Salts of the heavy metals such as 

 uranium, silver and mercury will severely inhibit the action of ptyalin. 



During the process of mastication the food is brought into intimate 

 contact with the saliva, but. does not have sufficient time to bring about 

 considerable digestion. The greatest activity of ptyalin takes place in 

 the fundus of the stomach, before the acidity of the stomach reaches the 

 level of concentration at which it inhibits the action of ptyalin. 



Action of Ptyalin. The ptyalin does not affect cellulose. It acts on 

 boiled starch much more readily than on native starch. It acts by bringing 

 about a process of hydrolysis whereby the large starch molecule, which 

 belongs to the suspension colloidal group, is broken up into smaller and 

 smaller molecules, passing through various stages of "colloidality," be* 



