258 HUMAN PHYSIOLOGY CHAP. 



on the moist mucous surface in the nose, and then stimu- 

 late the end organs of smell. The sense of smell aids 

 us in the selection of good foods and in the avoidance 

 of bad air. In some of the lower animals, as the blood- 

 hound, for example, this sense is much more highly 

 developed than in man. 



Taste and smell are so closely associated that it is 

 often difficult to separate them. Apple and onion 

 taste very differently to us, but they taste quite alike to 

 the person who has lost the sense of smell. Highly 

 flavored foods, alcohol, and tobacco tend to blunt these 

 senses. 



1. Blindfold a member of the class, and pinch his nostrils firmly, 

 and then have him try to distinguish between apple, potato, and 

 onion by the sense of taste. 



2. Chew some roasted coffee and notice carefully the taste and 

 odor. Repeat, but pinch the nostrils firmly all the time. What 

 difference do you observe ? .When a person has a cold in the head 

 some foods are tasteless. Can you tell why ? 



176. The Sense of Hearing. We come now to con- 

 sider one of the most important senses in man. How 

 dreary and gravelike the world would seem if we could 

 not hear the song of the birds, the hum of the bees, 

 and the voices of our friends ! The sense of hearing 

 can receive the waves of air caused by the vibrations of 

 a sounding body and give them meaning. What is 

 sound ? We shall try to find out. The vocal cords of a 

 person vibrate as the air is forced out of his lungs, and 

 produce a wavelike disturbance in the air. Between his 

 lips and your ear there are waves of air which you can 

 interpret, and so understand what he says. 



