122 DIGESTION 



15. These glands consist of clusters of very small pouches, 

 around which a delicate network of blood-vessels is arranged ; 

 they empty into the mouth by means of little tubes, or ducts. 

 The flow from these glands is generally sufficient to maintain 

 a soft and moist condition of the tongue and mouth ; but when 



they are excited by the pres- 

 ence and taste of food, they 

 pour forth the saliva more 

 freely. Even the mere thought 

 of food will at times cause the 

 saliva to flow, as when the ap- 

 petite is stimulated by the 

 sight or smell of some savory 

 article; so that the common 

 expression is correct that " the 

 mouth waters " for the favorite 



Fm. 27. THE HEAD OF A HORSE, showing articles of food. Anxiety and 

 the large salivary gland () ,, Its duct (6) , the f prevent i ts flow, and 

 muscles of mastication (e, d, e, f, and g) 



cause "the tongue to cleave to 



the roof of the mouth." In the horse, and other animals that 

 feed upon dry and coarse fodder, and require an abundant 

 supply of saliva, we find large salivary glands, as well as 

 powerful muscles of mastication. 



16. The mingling of the saliva with the food seems a simple 

 process, but it is one that plays an important part in digestion. 

 In the first place, it facilitates the motions of mastication, by 

 moistening the food and lubricating the various organs of the 

 mouth. ^Secondly, it prepares the way for other digestive 

 acts : by tjie action of the teeth, the saliva is forced into the 

 solid food) softens the harder substances, and assists in con- 

 verting the whole morsel into a semi-solid, pulpy mass, that 

 can be easily swallowed, and readily acted upon by other 

 digestive fluids. \ The saliva, also, by dissolving certain sub- 

 stances, as sugar and salt, develops the peculiar taste of each ; 

 whereas, if the tongue be dried and coated, they are taste- 

 is. The flow of saliva ? The thought of food ? Anxiety and grief ? Animals fed upon 



dry and coarse food ? 



1C. Importance of the process ? The first place ? The second ? The third ? 



