86 MAN AN ADAPTIVE MECHANISM 



In traumatizing the peripheral nerve trunks we 

 found that the type of injury had an important bear- 

 ing upon the response elicited. Thus the dragging, 

 pulling, tearing and contusing of nerve trunks produced 

 marked changes in the blood-pressure and respiration. 

 Thermal irritation caused an even greater rise in blood- 

 pressure ; but if the nerves were severed quickly with 

 a sharp knife, the resultant response was slight. There 

 were no hostile animals or agencies in the phylogenetic 

 environment whose instruments of attack approximated 

 the exquisitely sharp scalpel of the surgeon. 



Everywhere about the head and neck, as we have 

 noted, there is an adequate provision of self-defensive 

 mechanisms. Yet in a general traumatization of these 

 parts it was noted that apart from the keen sensibility 

 of the skin covering, there was no abundant distribu- 

 tion of contact ceptors. If the eyes, the conjunctiva, 

 the eyeball or the optic nerve was injured, there was occa- 

 sionally a slight though scarcely perceptible change in 

 blood-pressure. The adaptive response here is confined 

 chiefly to winking, which exerts but slight demand on the 

 general muscular system, hence no circulatory changes 

 are seen. But such injuries as the contusion, laceration 

 or dilatation of the nostrils were met promptly by a 

 distinct rise in the blood-pressure. In this case a vital 

 function of the body respiration was threatened. 

 The response was equivalent to that frantic fighting 

 to be free which follows any attempt to obstruct the 

 nostrils of any animal or of man. For the same reason, 

 mechanical injury of the interior structures of the throat 

 and mouth produces a change in blood-pressure, when 

 injury to the respirator)' function is threatened. The 



