DIGESTION IN THE MOUTH 303 



classification is more logical, but the latter is more convenient and more gen- 

 erally used. 



TABLE or DIGESTIVE ENZYMES. 

 Amylolytic. 



Ptyalin of saliva, and amylopsin of pancreatic juice, change starch to maltose. Malt- 

 ase in the saliva, and pancreatic juice in the small intestine, change maltose to dextrose. 

 Lactase splits lactose to galactose and dextrose, and invertase splits cane-sugar to levulose 

 and dextrose in the small intestine. 



Lipolytic. 



Steapsin or lipase, found in the pancreatic juice, splits neutral fats into glycerin and 

 fatty acid. 



Proteolytic. 



Pepsin of the gastric secretion, and trypsin of the pancreatic secretion, change pro- 

 teids to proteoses and peptones, trypsin breaking the proteid down to simpler nitrog- 

 enous products. Erepsin of the intestine splits peptones to simpler products. 

 Coagulating. 



Rennin of the gastric juice coagulates milk. 

 Activating. 



Enterokinase of the intestinal juice converts trypsinogen to trypsin. (Thrombokin 

 of the blood is of this class.) 



DIGESTION IN THE MOUTH. 



The food is received into the mouth, and is subjected to the action of the 

 teeth and tongue, being at the same time mixed with the first of the digestive 

 juices, the satvva. It is then swallowed, and, passing through the pharynx 

 and esophagus into the stomach, is subjected to the action of the gastric 

 juice, the second digestive juice. Thence it passes into the small intestines, 

 where it meets with the bile, the pancreatic juice, and the intestinal juices, all 

 of which exercise a digestive influence upon the portion of the food not already 

 digested and absorbed. In the large intestine some further digestion and 

 absorption take place, and the residue of undigested matter leaves the body 

 in the form of feces. 



Mastication. The act of mastication is performed by the biting and 

 grinding movement of the lower range of teeth against the upper. The 

 simultaneous movements of the tongue and cheeks assist by crushing the 

 softer portions of the food against the hard palate and gums, thus supplement- 

 ing the action of the teeth, and by returning the morsels of food to the action 

 of the teeth as they are squeezed out from between them until they have been 

 sufficiently chewed. 



The simple up-and-down or biting movements of the lower jaw are per- 

 formed by the temporal, masseter, and internal pterygoid muscles, the~a<?tioff 

 of which in closing the jaws alternates with that of the digastric and other 

 muscles passing from the os hyoides to the lower jaw, which open the jaws. 

 The grinding or side movements of the lower jaw are performed mainly by 

 the external pterygoid muscles, the muscle of one side acting alternately with 



