FUNCTIONS OF THE SKIN 93 



entire body, are found in rings around hair follicles, the 

 hairs acting like levers can thus give rise to the sense 

 of pressure or touch when nothing has touched the skin, 

 as when an insect crawls over the hair or when the wind 

 moves it. 



Certain areas, like the tips of the fingers, and the tip 

 of the tongue are very abundantly supplied with touch 

 nerves, while other parts, like the middle of the back, 

 have pressure spots only at comparatively wide inter- 

 vals, and it would seem that the number may be in- 

 creased by use, as is seen in the delicate sense of touch 

 possessed by the blind, or in the fingers of a trained sur- 

 geon. At least the nerve terminals may be educated and 

 become more sensitive. Skin sensations are as much or- 

 gans of special sense as the eye or ear and capable of 

 as much improvement by training. From this it would 

 appear that some persons not only cry out more than 

 others under the effects of pain, but that they actually 

 suffer more pain. 



Two modifications of cutaneous sensibility, itching and 

 tickling, deserve particular mention. Neither is clearly 

 explained, but it would appear that itching is never a 

 normal nerve impulse, but is always the result of in- 

 jury or disease; while tickling seems to be a modifica- 

 tion of tactile sensation due to rapidly repeated stim- 

 ulation. Some observers think itching a mild stimula- 

 tion of nerves conveying painful sensation. 



The function of the mammary gland will be described 

 with the reproductive organs. 



