46 FEEDING ANIMALS. 



some chemical action upon the food after it reaches the 

 stomach. 



A gland may be defined as an organ, the function of 

 which is to separate from the blood some particular sub- 

 stance, and discharge it through an excretory duct, whose 

 internal surface is continuous with the mucous membrane. 

 A simple gland is merely a follicle of the mucous mem- 

 brane, and a collection of these follicles is a compound 

 gland, and if the groups of which it is composed are 

 loosely bound together like clusters of grapes, it is called 

 conglomerate, as in the salivary glands ; but if united into 

 a solid mass, such as the liver, it is called a conglobate 

 gland. Inside of these follicles are cells, which are the 

 active agents in the secreting process, whilst they are sur- 

 rounded by a network of capillaries in which the blood 

 circulates and furnishes the materials for these secretions. 

 These cells are so minute as to require the aid of a micro- 

 scope for their examination. 



The salivary glands are five in number four of them in 

 pairs : 1. The parotid gland, which is much the largest, is 

 situated at the posterior angle of the lower jaw, or near 

 the ear. 2. The maxillary or sub-maxillary gland is on the 

 interior central border under the lower jaw. 3. The sub- 

 lingual gland is situated under the tongue. 4. The molar 

 glands are situated parallel to the molar arches. 5. The 

 labial (or lip glands) and the palatine glands (under mu- 

 cous covering of the soft palate), these latter are mostly 

 single follicles, and each has a separate excretory duct dis- 

 charging its secretion into the mouth. The saliva is an 

 extremely watery fluid, having only from 6 to 8 parts of 

 solid matter in 1,000 parts, but this solid or saline matter 

 plays an important part in digestion. There is an ac- 

 tive ferment, called ptyalin, in saliva, which, although 

 found in very small proportion, possesses the property of 

 changing starch into sugar in the process of digestion, 



