CHAPTER XVI 

 COORDINATION 



It seems that Nature, after elaborating mechanisms to meet partic- 

 ular 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 variations in the 

 equilibrium of its own matter and energy — it is not strange that 

 the cells of an organism mutually influence 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 interplay 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 inter- 

 communication 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 importance of the 

 chemical control of bodily processes has gradually 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 do little more than cite the 

 specific action of individual hormones as examples of the general 

 method of chemical regulation which their study, endocrinology, 

 is revealing. (Pp. 159, 169, 192.) 



Certain hormones are elaborated by special cells embedded in 

 organs, such as the pancreas, intestine, and reproductive organs, 

 largely devoted to other functions. Other hormones are secreted 

 by organs whose sole function is their production, such as the 

 various ductless, or endocrine, glands. 



As an example of a hormone secreted by specialized cells within 

 the tissue of an organ devoted primarily to other functions, we may 



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