'20 THE NERVOUS SYSTEM AND ITS CONSERVATION 



po-ing tli:tt no process of contraction or secretion lakes 

 phu't 1 save as the nervous system initiates it. This is very 

 far from being the case. 



All the branches of the nerves which enter the sub-tancc 

 of the heart may be cut, but the heart will continue to 

 beat. Hence, we cannot believe that each beat of tin- 

 heart is dictated by the efferent elements of the coordinat- 

 ing system. The power to make rhythmic contractions 

 is resident in the organ itself; we say that it is automatic. 

 In a less striking, but still positive, way other organs dis- 

 play a tendency to activity when removed from central 

 command. This is demonstrable for the stomach, the 

 intestine, and the urinary bladder. The contractile tis- 

 sues which enter into the make-up of these viscera must 

 be said to have a degree of automaticity. 



When an organ has this disposition to be active on its 

 own account it will be seen that the nervous system may 

 exert a twofold influence upon it. The native, local 

 process may be accelerated beyond its average rate of 

 progress, or it may be restrained more or less radically. 

 We say that tissues which possess the automatic property 

 may exhibit either excitation or inhil>ili<t when the nervous 

 system modifies their inherent tendency. It is probably 

 just to claim t hat both with t he heart and with the alimen- 

 tary tract inhibitory effects are more frequently witnessed 

 than are those which are clearly excitatory. If one is 

 inclined to question this, on the ground that quickening 

 of the heart-beat in exercise is a daily experience, it may 

 be answered that this quickening is known to be to a 

 great extent the ir/t/iilniiral of an inhibition previously 

 operative. \Yitlidrawal of inhibition is a form of counter- 

 feit stimulation which will repeatedly call for considera- 

 tion in later paragraphs. The slowing of the heart after 

 exercise may be a more positive instance of nervous inter- 

 vention than the hastening of its action, which -eems so 

 much more impre ive. 



A- for the alimentary canal, it ha> become well recog- 

 nixed that it- movement.- are actuallv ob-erved to better 



