92 PHYSIOLOGY TOR NURSES 



Iii addition to these active and important excretory 

 functions of the skin, there is a slight power of remov- 

 ing carbon dioxide. 



Cutaneous Sensations. Everyone is aware of a capac- 

 ity to feel; i.e., a sense of touch, or tactile sense; and to 

 distinguish between rough and smooth, sharp and blunt, 

 hot and cold, heavy and light objects, etc. These are 

 among our cutaneous sensations, though the last two are 

 more properly muscle sensations. The capacity to feel 

 pain is more widely distributed than the other skin sen- 

 sations. 



Nerves which convey information to the brain from 

 any portion of the body are called sensory, or afferent, 

 and each nerve ending responds to but one stimulus; i.e.. 

 can carry information of but one kind. Thus if the 

 nerve of sight is cut, no pain is felt, but only a riash 

 of light will be recognized by the brain. 



Observation has proved that there are four stimuli 

 which can excite the nerves distributed to the skin, 

 which will convey four kinds of information to the 

 brain. These four sensations are heat, cold, pressure or 

 touch and pain. Careful experiments have shown that 

 minute areas of skin are sensitive to one or another of 

 these stimuli and to no other. Such areas are designated 

 lieat spots, cold spots, pressure or pain spots. If one 

 touches, with a delicate instrument, a cold spot, a sen- 

 sation of cold will be experienced, even if the instrument 

 itself is u'unHf'r Hum the skin.. Cold spots are more nu- 

 merous than warm; pressure points more numerous than 

 either and pain spots the most numerous of all. Some 

 portions of the body envelope, like the membrane cover- 

 ing the eyeball, have no nerve spots except those of 

 pain, which are present in great numbers. Pressure 

 spots, supposed to number about half a million for the 



