THE SPECIAL SENSES 



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339. The Special Senses. There are certain avenues by 

 which we get information concerning the world around us. 

 In other words, we are provided with a number of special 

 senses by means of which information is furnished us regard- 

 ing outward forces and objects. 



These special sense organs, or "gateways of knowledge," 

 are the skin, the chief organ of touch and temperature ; the 

 tongue, the chief organ of taste ; the nose, of smell ; the ear, 

 of hearing ; and the eye, of sight. 



340. Touch. The sense of touch is the 

 most widely extended of all the senses, 

 and perhaps the simplest. It has its 

 seat in the skin all over the body and in 

 the lining of the mouth and nasal pas- 

 sages. By this sense of touch we can 

 tell whether a body is hard or soft, hot 

 or cold, rough or smooth. 



We have learned about the thousands 

 of tiny hillocks called papillae, which form 

 rows of very thick ridges on the tips of 

 the fingers (Sec. 254). 



Now, besides a tiny artery and vein, finer than the finest 

 hair, there is in each papilla the end of a sensory nerve. 

 Where the sense of touch is most delicate, the papilla is 

 found to contain a little oval bulb called the touch corpuscle. 



NOTE. There is another sense, commonly known as the muscular 

 sense, which enables us to judge the weight of different bodies accord- 

 ing to the muscular effort required to lift or hold them. This sense 

 becomes so highly developed by use that shopkeepers and others who 

 sell various articles by weight can often tell the weight of a body by 

 simply balancing it in their hands. 



The sense of heat and cold, or sensation of temperature, may also 

 be regarded as a distinct sense. 



FIG. 151. A Papilla 



of the Skin, with a 

 Touch Corpuscle. 

 Highly magnified. 



