CONTACT CEPTORS 91 



injury, but contact ceptors have been evolved from 

 within by the forces of pressure or obstruction. 



This study of the distribution of the pain areas in 

 the body enables us to draw valuable conclusions in 

 regard to the evolution of functional processes in the 

 organism by factors in the environment. To recapit- 

 ulate : The response to physical trauma is deter- 

 mined by two things : (1) By the type of injury in- 

 flicted, that is, whether or not it approximates 

 the injury inflicted during phylogeny; (2) By the 

 region traumatized, that is, whether or not it was 

 exposed to injury throughout phylogeny. We see 

 that injuries from artificial, extra-natural agencies, 

 such as keen-bladed knives, fast bullets, radium emana- 

 tions and the X-ray cause little or no pain or other 

 response, while injury by tearing with blunt instru- 

 ments, simulating the commonest type of phylogenetic 

 attack with teeth and claws, or by bruising and crush- 

 ing environmental contact, causes a swift and power- 

 ful response and pain. 



We see that areas which have been commonly pro- 

 tected from contact with environment by an impervious 

 outer layer of bone or flesh, such as the brain and the 

 heart, to which penetration would have meant instant 

 death, have developed no protective pain mechanisms, 

 while areas which have been continuously exposed to 

 injurious forces, such as the surface and extremities, 

 are plentifully supplied with contact ceptors. Thus, 

 deep and protected areas and organs, such as the liver, 

 spleen and kidneys, are, like the heart, lungs and brain, 

 almost devoid of contact ceptors : the back and spine 

 are but sparsely supplied, while the exposed surfaces 



