THE RECEPTOR SYSTEM 



213 



The pain nerves of the skin do not seem to be provided with 

 special end organs but to end nakedly among the cells of the 

 epidermis. Such a mode of termination accords with the low 

 irritability of the pain mechanism and with its absence of adapta- 

 tion to particular forms of energy, since nerve-tissue proper ex- 

 hibits these same qualities. 



The interior of the Body, in certain regions at least, seems to 

 be provided with special pain receptors. These are the Pacinian 

 corpuscles (see Fig. 67). They are specially numerous in the mesen- 

 tery, the connective tissue membrane 

 which supports the abdominal viscera. 



Pains can be localized, though only 

 imperfectly, and the less perfectly the 

 more severe they are. The exact place 

 of a needle prick after removal of the 

 needle (so that there is no guiding 

 concomitant touch sensation) cannot 

 be recognized as well as a pin touch 

 on the same region of the skin, but 

 still fairly well; while the acute pain 

 caused by a small abscess (bone felon) 

 under the periosteum of a finger bone 

 is often felt all over the forearm; and 

 a single diseased tooth may cause pain 



felt over the whole of that side of the FlG . 6 7._ A Pacin ian corpus- 

 face. cle magnified. 



Many internal pains instead of being felt as coming from the 

 organ where they originate are referred to areas of the skin. So 

 constant is this misreference that the physician is able to judge 

 of the seat of many disturbances from the particular skin areas 

 that exhibit tenderness. The explanation of this misreference 

 of internal pain to the skin is not easy to make. It has been sug- 

 gested that the nerve-paths over which internal pain reach the 

 body sense-area of the cortex lie close to those of pains from cer- 

 tain skin areas; and that since painful skin stimulation is much 

 more common than internal pains, the brain interprets all im- 

 pulses reaching it over a restricted nerve-path as coming from 

 the particular skin area whose nerve-path forms part of the whole 

 nerve-path in question. 



