CHAPTER III 



ADAPTATION BY MEANS OF CONTACT CEPTORS 



The Receptor Organs 



IN the foregoing chapter we stated our viewpoint 

 that the nervous system of man, like other organic 

 structures, is the product of the selective adaptation 

 of the organism to its environment; and that the 

 nervous system acts as a conducting mechanism for the 

 specific energies or stimuli of the environment which 

 evoke the adaptive reactions of the organism. For the 

 reception and transmission of environmental stimuli 

 receptor organs have been evolved. A study of the 

 distribution and relative activities of these mechanisms 

 epitomizes the story of the adaptation of the whole 

 organism. In that of man and of all other multi- 

 cellular organisms there are presented to the en- 

 vironment two fields of contact in which receptor 

 organs are implanted : an outer surface of skin 

 and mucous membranes, which are exposed to every 

 vicissitude of climate and contact, and inner organs 

 and connective tissue, which are partially screened 

 from the outer environment, but are subject to a vari- 

 ety of physical and chemical changes within the or- 

 ganism itself, these changes, however, being primarily 

 induced by the larger reactions initiated by the cep- 

 tors of the outer surface. Imbedded in the cellular 



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