38 THE HUMAN BODY 



The Conductive System. Organs for making movements and 

 organs for receiving impressions from the surroundings are not of 

 themselves adequate to the maintenance of adaptation. It is 

 necessary that the information gained by the sense-organs be trans- 

 mitted to the muscles so that their movements may correspond to 

 the requirements of the situation. This function is performed by 

 the nervous system. The conduction of stimuli from sense-organs 

 to muscles is not, however, a simple matter. Impressions are con- 

 tinually coming into the Body by way of a number of different 

 channels. Movements must be made not in obedience to any one 

 of these impressions by itself but for the advantage of the whole 

 Body as indicated by all of them taken together. To this end a 

 certain part of the nervous system is adapted for receiving all 

 sorts of incoming stimuli and before passing them on to the motor- 

 organs combining and modifying them to produce the best results. 



While for purposes of convenience, the conductive system is 

 classed as one of the adaptive mechanisms, we need to bear in 

 mind that nervous co-ordination, for which this system is the 

 agency, although concerned primarily with direct adaptation, has 

 also much to do with the control of those activities which are pri- 

 marily concerned with maintenance and only indirectly adaptive. 



Maintenance Systems. The systems which are not imme- 

 diately concerned in the adaptation of the Body to its environment 

 but which serve rather to keep it in proper condition for activity 

 may next be considered. 



Activity in the Body involves the manifestation of energy, and 

 in its energy relations the Body is on exactly the same plane as 

 any machine; it is without power to manufacture energy, and 

 must receive whatever energy it obtains from without. The ulti- 

 mate source of the Body's energy is chemical, being received 

 in the complex substances which serve as food. This energy 

 is made available for the use of the Body chiefly through the 

 process of oxidation. Every living cell in the Body must share 

 in this process, for the energy manifestations of the Body as a 

 whole are simply the sum-total of those of its component cells. 



The systems which are concerned with the maintenance of ac- 

 tivity have, then, the task of furnishing to each cell of the Body 

 oxidizable substance and oxygen; they must provide for making 

 good the wear and tear of the cells themselves; and they must 



