THE RECEPTOR SYSTEM 177 



served In cases of spinal cord disease: and in a certain stage of 

 chloroform or ether narcosis the patient feels the surgeon's hand 

 or his knife where it touches the skin, but he experiences no pain 

 when deeper parts are cut. 



Such considerations seem to lead to the conclusion that the 

 nerve-fibers and receptors concerned with painful sensations are 

 quite distinct from those of the other senses. If that be so we 

 must assume that there are " pain " fibers very widely distributed 

 over the skin and through most other parts of the Body. In 

 accident or disease these are stimulated powerfully enough to 

 arouse perception and imperiously call attention to danger. 



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

 spebial 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 

 mesentery, 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 face. 



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- 



