August 29, 1913] 



SCIENCE 



285 



the muscular exertion of which it is the 

 representative. 



That this nerve mechanism may effect- 

 ively carry out its twofold function, first, 

 of self-adaptation to meet adequately the 

 increasingly complicated stimuli of en- 

 vironment; and second, of in turn adapt- 

 ing the motor mechanism to respond ade- 

 quately to its demands, there have been 

 implanted in the body numerous nerve 

 ceptors — some for the transmission of stim- 

 uli harmful to the mechanism — nocicep- 

 tors; some of a beneficial character — bene- 

 ceptors; and still others more highly spe- 

 cialized, which partake of the nature of 

 both bene- and nociceptors — the distance 

 ceptors, or special senses. 



A convincing proof that environment 

 has been the creator of man is seen in the 

 absolute adaptation of the nociceptors as 

 manifested in their specific response to 

 adec^uate stimuli, and in their presence in 

 those parts of the body only which through- 

 out the history of the race have been most 

 exposed to harmful contacts. We find they 

 are most numerous in the face, the neck, 

 the abdomen, the hands and the feet ; while 

 in the back they are few in number, and 

 within the bony cavities they are lacking. 



Instances of the specific responses made 

 by the nociceptors might be multiplied in- 

 definitely. Sneezing, for example, is a 

 specific response made by the motor mech- 

 anism to stimulation of the nociceptors in 

 the nose, while stimulation of the larynx 

 does not produce a sneeze, but a cough; 

 stimulation of the nociceptors of the stom- 

 ach does not produce cough, but vomiting; 

 stimulation of the nociceptors of the intes- 

 tine does not produce vomiting, but in- 

 creased peristaltic action. There are no 

 nociceptors misplaced; none wasted; none 

 that do not make an adequate response to 

 adequate stimulation. 



Another most significant proof that the 



environment of the past has been the cre- 

 ator of the man of to-day is seen in the 

 fact that man has added to his environ- 

 ment certain factors to which adaptation 

 has not as yet been made. For example, 

 heat is a stimulus which has existed since 

 the days of prehistoric man, while the X- 

 ray is a discovery of to-day; to heat the 

 nociceptors produce an adequate response; 

 to the X-ray there is no response. There 

 was no weapon in the prehistoric ages 

 which could move at the speed of a bullet 

 from the modern rifle; therefore, while 

 slow penetration of the tissues produces 

 great pain and muscular response, there is 

 no response to the swiftly moving bullet. 



The response to contact stimuli then de- 

 pends always on the presence of nocicep- 

 tors in the afl^ected part of the body and to 

 the type of the contact. Powerful response 

 is made to crushing injury by environ- 

 mental forces; to such injuring contacts as 

 resemble the impacts of fighting; to such 

 tearing injuries as resemble those made by 

 teeth and claws. On the other hand, the 

 sharp division of tissue by cutting produces 

 no adaptive response; indeed, one might 

 imagine that the body could be cut to 

 pieces by a superlatively sharp knife ap- 

 plied at tremendous speed without ma- 

 terial adaptive response. 



These examples indicate how the history 

 of the phylogenetic experiences of the hu- 

 man race may be learned by a study of the 

 position and the action of the nociceptors 

 just as truly as the study of the arrange- 

 ment and variations in the strata of the 

 earth's crust discloses to us geologic his- 

 tory. 



These adaptive responses to stimuli are 

 the result of the action of the brain cells 

 which are thus continually played upon by 

 the stimuli of environment. The energy 

 stored in the brain cells in turn activates 

 the various organs and parts of the body. 



