CHAPTER IV 



ADAPTATION BY MEANS OF CHEMICAL CEPTORS AND 

 CHEMICAL ACTIVITY 



THE division of the receptor mechanisms of the 

 body into contact, chemical and distance ceptors indi- 

 cates the adaptive power of the organism as evinced 

 (1) by local cellular masses; (2) by the individual 

 cells as separate entities; (3) by the organism as a 

 whole. For, as we have seen, the response to heat 

 pain by the removal of the injured part from the in- 

 juring contact is essentially the response of a part of 

 the organism for the good of the whole. In like man- 

 ner, such protective reactions as the response to excita- 

 tion of the chemical ceptors in the stomach by food ; 

 in the respiratory centers by acidity; in the cortex 

 by foreign proteins ; in the mouth and nose by food 

 and food particles, are responses of specialized tissue 

 for the good of the whole animal, these reactions dif- 

 fering in kind but not in principle from reactions to 

 excitation of the contact ceptors. Later, we shall 

 see that the response to excitation of the distance 

 ceptors is the response of the integrated animal for the 

 good of the species. 



The existence of chemical mechanisms of adaptation 

 indicates the existence of an inner activating medium 

 which is distinct from the outer activating environ- 

 ment. As the contact ceptors represent the factors 



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