346 . ELEMENTARY PHYSIOLOGY less. 



5. The Skin as a Sense -Organ.— The sensations which 

 originate in the skin and tlie parts which lie under it are 

 those of pressure, heat, cold, and pain. These sensations 

 are difficult to analyse. 



Take for instance the sensation of pressure. If my 

 hand is held out horizontally with the palm upwards and 

 another person makes a considerable but unsuccessful 

 effort to lower it by pressing the palm downwards, I can 

 appreciate that pressure and even make an estimate of 

 it. This I could do were there no skin on my hand. I am 

 really appreciating the strain which is put upon my 

 muscles and tendons in successfully resisting the pressure. 

 The information is sent up to my brain from sense-organs 

 situated in the tendons, muscles, and joints. In contrast 

 to that experiment the following may be performed. The 

 skin on the palm of my hand may be just touched lightly 

 with a blunt object, or some cotton wool, and I may be 

 asked if, without using my eyes, I can appreciate and 

 locate the touch. In this experiment I am also appreci- 

 ating sensations of pressure, but the sensations are quite 

 different in kind as well as in degree from those estimated 

 in the former experiment. The sense-organs which feel 

 the cotton wool are in the skin. At once then we can 

 divide our appreciation of pressure into two quite different 

 faculties which are termed respectively the deep and the 

 superficial sensibility accoi'ding as they are located in 

 the parts below the skin or in the skin itself. 



Even in the skin however there seems to be more 

 than one mechanism for the appreciation of any par- 

 ticular type of sensation (tactile sensation, heat, cold, or 

 pain). 



Just as in a microscope we have a "coarse" and "fine" 

 adjustment for focussing the slide, so in the skin we have 

 a coarse and a fine adjustment for the feeling of, say, 

 pain. With the coarse adjustment only we get what 

 we may speak of as a blurred image of pain, of heat or of 



