THE ORGANS OF SENSE 305 



the body. These sensations doubtless have their own 

 separate nerves corresponding to little areas called heat 

 spots and cold spots which, when stimulated, yield each 

 its own sensation of heat or cold respectively. Menthol 

 has the property of stimulating the cold spots and of mak- 

 ing the skin feel cold, although in reality it may be quite 

 warm. Pain is a definite sensation which is aroused 

 when the tissues of the body are injured. 



The sensation of taste is aroused by the stimulation of 

 the taste buds of the tongue. There are a limited number 



FIG. 217. Nasal cavity. i, olfactory nerve with its branches 

 shown in 2; 3 and 4, turbinated bones; 5, fifth cranial nerve. (After 

 Marshall.) 



of true sensations of taste, i.e., sweet, bitter, sour, salt; 

 much of what we call tastes are really odors which are 

 caused by substances arising through the pharynx and 

 stimulating the olfactory nerves. This is why holding the 

 nose when certain substances are being chewed and swal- 

 lowed, and thereby preventing the air from freely entering 

 the nasal cavity from behind, tends to make us unaware 

 of their flavor. 



The eyes are among the most complex and delicately 

 adjusted organs of the body and they have long excited 

 wonder and admiration on account of the perfection of 

 their mechanism. The eyes are freely movable within 



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