SENSE OKGANS AND SENSATIONS 



259 



The afferent nerves of cold and warmth not only carry 

 into the brain those impulses which give rise to the corre- 

 sponding sensations but also serve as one important means 

 of stimulating the reflexes which help to regulate heat 

 production and heat output (see Chap. XII). 



23. The sense of position. The expression "the five senses" 

 has become proverbial, and comes from the time when sight, 

 hearing, taste, smell, and touch were the recognized special 

 senses. To-day, however, we must add to 

 these not only warmth and cold but still 

 others, most conspicuous among which is the 

 sense of position. When the eyes are closed 

 we are aware of the position of the various 

 parts of the body. We know whether the 

 arm is bent at the elbow or straight ; whether 

 the head is looking forward or is turned to 

 one side or the other. And while we are 



aware of these things, partly from tactile 



. 8 ' F . J . . FIG. 103. A tac- 



sensations, there is conclusive evidence that ti i e cor puscle in 



afferent impulses from the muscles, tendons, one of the papil- 



and joints also play an important part in lse of t ? e dermis ] 



, , an end organ of 



the result the sense of touch 



When one is blindfolded and lies flat on a 

 revolving table which can be turned noiselessly in one direc- 

 tion or the other, the subject of experiment can form fairly 

 correct judgments as to the angle and direction through 

 which the table is turned. Here there is no change of char- 

 acter either in the tactile impulses or in those from the mus- 

 cles, tendons, and joints, for the subject of experiment lies 

 still and is only passively moved. It is believed that in this 

 case the sensations in question come from the movements of 

 the lymph in portions of the inner ear. One part of this, 

 the cochlea, is undoubtedly concerned with the perception of 

 sound ; but another part, the three semicircular canals, are 

 now believed to be end organs of this sense of position. 



