THE SYMPATHETIC SYSTEM 3OI 



connections, yet all these processes nutritive in nature 

 have their normal activity seriously impaired by with- 

 drawal of the sympathetic influence. 



The chief vaso-motor center is in the medulla, though ac- 

 cessory centers exist also in the cord ; all vaso-motor fibers 

 pass out from these centers and leave the cerebro-spinal 

 axis with the cranial or spinal nerves. 



The most usual mode of action of the vaso-motor nerves 

 is reflex, as when the mucous membrane of the stomach be- 

 comes hyperemic upon the introduction of food ; or when the 

 salivary secretion increases during mastication, or even 

 sometimes at the sight or thought of food; or when emo- 

 tions are evidenced by paling or blushing. 



Raising blood-pressure by stimulating the vaso-constric- 

 tors and lowering it by stimulating the vaso-dilators are sim- 

 ply mechanical results, and require no comment. 



Sleep. Sleep is closely associated with vaso-motor action. 

 Every part of the body has a function to perform, but it 

 must have some rest from that performance or it will begin 

 to act inefficiently and finally cease altogether. For most 

 organs these periods of rest occur at approximately uniform 

 intervals, as in case of the stomach, heart or respiratory 

 muscles ; but notably in case of the involuntary muscles these 

 periods of repose have no regularity i. e., a person exer- 

 cises them at no regular time except by accident of occupa- 

 tion or otherwise. But, in any case, there comes a time 

 when repose must be had, for during activity the destructive 

 processes far exceed the constructive, and in order for the 

 balance to be preserved there must be a time when the op- 

 posite is true. 



Now we may say that it is the function of the brain to fur- 

 nish consciousness if we can allow that consciousness em- 

 braces all the various manifestations of nerve force peculiar 

 to the brain. For the brain to suspend this function at fre- 

 quent intervals like the heart (e. g.) would be manifestly im- 

 possible if one is to do any consecutive work depending upon 



