130 PHYSIOLOGY AND TEMPERANCE. 



on the alert and ready to warn him of anything disagreeable, 

 offensive or injurious. By it he knows the appetizing qualities 

 of many foods. By it he enjoys the fragrance of the flower 

 and of choice perfume. 



It is not always necessary to bring the substance close to 

 the nose to detect its odor. Some smells can be recognized 

 at a great distance from their source. Invisible particles 

 float in the air and fall upon the sensitive membrane of the 

 nose. Some persons have not as acute a sense of smell as 

 others. Like all other faculties, it can be educated. Certain 

 tribes of Indians, who rely in a great measure upon this 

 organ, have an extraordinary sense of smell. The lower 

 animals, also, differ in the acuteness of this organ. The dog, 

 especially the hound, has a wonderful faculty for smelling. 

 He will follow on the trail of a fox for miles guided only by 

 the scent. 



5. Other Uses. The cavity of the nose has other 

 functions than those mentioned. It is the outlet for the 

 secretions from the cavities in the cheek bones. Also, the 

 cavity between the plates of bone in the forehead opens into 

 the nose and is relieved of its secretions. Likewise, when 

 the secretion of water in the eyes is excessive, but not 

 sufficient to overflow in the form of tears, it is carried from 

 the inner corner of the eye by a small canal into the nose. 



6. The Sense of Sight. The organ of sight is lodged 

 in a cavity made up of thin plates of bone joined together. 

 At the bottom of this cavity, or socket, as it is called, is a 

 small opening through which the optic nerve passes from the 

 brain to the eye. The eye-ball, fitly so called, is about an 

 inch in diameter. It is composed of the crystalline lens ; a 

 jelly-like substance, called the vitreous humor, situated behind 

 Jhe lens ; the 'aqueous humor in front, and the iris which acts 

 as a curtain, through the centre of which is an opening, 



