CHAPTER XIV 



COORDINATION IN ANIMALS 



It seems that Nature, after elaborating mechanisms to meet 

 particular vicissitudes, has lumped all other vicissitudes into 

 one and made a means of meeting them all. Mathews. 



SINCE a primary attribute of protoplasm is irritability 

 the power of responding to environmental changes by changes 

 in the equilibrium of its own matter and energy it is not 

 strange that the cells of an organism mutually modify each 

 other's activities and reciprocal interrelationships have been 

 established during their long evolutionary history. The 

 various cells, tissues, organs, and organ systems are unified 

 into an organism by what may be called the chemical inter- 

 play between its various parts, which is made possible by the 

 facilities for distribution afforded by the circulatory system; 

 and also by the directing influence of the nervous system 

 which supplies a central station with lines for instantaneous 

 intercommunication with every part of the body. 



A. CHEMICAL COORDINATION 



It is only with the recent increase in knowledge of the 

 general problem of metabolism that the far-reaching impor- 

 tance of the chemical control of bodily processes has grad- 

 ually been brought to the fore. Although we may properly 

 think of the various chemical regulators, or HORMONES, as 

 forming a coordinating system in so far as their collective 

 action has such a result, in the present stage of our knowledge 

 it is possible to cite only the specific action of individual hor- 



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