16 Insalivation. 



course. The remaining part of the gullet passes 

 through the chest, and is called the thoracic por- 

 tion. The passage of food through the pharynx 

 and gullet is termed deglutition or swallowing. 



INSALIVATIOX. 



The mouth is abundantly supplied with fluid 

 for the purpose of lubricating its surfaces during 

 motion in mastication. It also possesses peculiar 

 solvent and chemical actions upon alimentary 

 matters introduced, and thus effects special 

 changes in their constitution, of vital importance 

 to digestion and assimilation. 



Saliva is the name given to this fluid, and is 

 the produce of glands in the vicinity, the largest, 

 the parotid gland, being placed below the ear 

 behind the angle of the lower jaw. In addition 

 there are others of a smaller character situated 

 beneath the tongue, between the sides of the 

 jaw, inside the lips and other parts ; all of which 

 separately contribute important properties to the 

 fluids which mix in the mouth, whence they are 

 conveyed by appropriate tubes or ducts. 



The solvent action of saliva depends upon the 

 presence of peculiar salts and a principle called 

 ptyalin by scientific men, and is easily demon- 

 strated by placing food within the mouth. It is 

 also found to act efficiently when collected in 

 suitable vessels and brought into contact with 



