THE EEASOX "WHY. 



' And the Lord said unto him, Who hath made man's mouth P or who maketh 

 the dumb, or the seeing, or the blind ? have not I the Lord f " EXODUS rv. 



Because the glands, which are buried in the muscles of the 

 mouth, and which in their form are much like bunches of currants, 

 are always full of salivary secretion. There are nerves which aru 

 distributed from the brain to these glands, and when other nei"ves 

 which belong to the senses of taste, of sight, or of feeling, are 

 excited by the presence of food, a stimulus is imparted to the 

 salivary glands, through the nerves that surround them, their ceHs 

 collapse, and the juice which they contain is poured out through 

 their stems, or ducts, into the mouth. 



874. Hoto do we know that impressions imparted to one 

 set of nerves, may be imparted to another set, so as to put any 

 particular organ in action. 



Because very frequently the mere sight of rich fruit, or a3id sub- 

 stances, will cause the saliva to flow freely. In this case it is 

 evident that the salivary glands could not see or know that such 

 substances were present. An impression must, therefore, be made 

 upon the brain, through the organ of vision, and the desire to 

 taste the substances being awakened, a nervous stimulus is 

 imparted to the glands of the mouth, and they at once commence 

 their action, as if food were present. 



875. Why does food descend into the stomach ? 



Because, after the teeth, the tongue, and the muscles of the 

 mouth generally, have rolled the food into a soft bolus, it is con- 

 veyed to the back of the mouth, where it is set upon the opening of 

 the throat (oesophagus). It does not then descend through the 

 throat by its own gravity, because the throat is generally in a com- 

 pressed or collapsed state, like an empty tube ; and we know that 

 persons can eat or drink when with their heads downwards. The 

 (Esophagus is formed of a number of muscular threads, or rings, 

 and each little thread is like a hand ready to grasp at the morsel 

 that is coming. As soon as the bolus is presented at the top of the 

 throat, these little muscular hands lay hold of it. and transmit it 

 downwa d, passing it from one to another, until it is conveyed 

 through the long passage, to the door of the stomach, which it 

 enters. 



