WHOLE NERVOUS SYSTEM. 603 



which give information of what is going on, while 

 the nerves operate as messengers that convey 

 orders from the chief to the ranks, and bring back 

 information in regard to their condition. So long 

 as the commander fulfils his duty, the evolutions 

 of the army are performed with order and intel- 

 ligence ; but should he be slain or wounded, and 

 his place not taken by another chief, or should 

 his means of communication with his subordinate 

 officers be cut off, the operations of the army be- 

 come irregular, confused, and inefficient, because 

 no longer guided by superior intelligence. In 

 like manner, when the sentient power of the 

 brain has been destroyed by suffocation, strangu- 

 lation, or a violent concussion, the locomotive mus- 

 cles contract spasmodically, because no longer 

 directed by the organ of thought. 



So far is the brain from being the source of 

 moving power in the animal economy, that arte- 

 rial blood is more essential to its vitality than to 

 any of the other organs ; for if the carotid and 

 vertebral arteries be divided or tied, it dies al- 

 most immediately, and long before the heart 

 and other muscles cease to contract. The reason 

 of which is, that the brain is supplied with five 

 or six times more blood in proportion to its mag- 

 nitude, than the general system corresponding 

 with its exalted vitality, and the important office 

 it has to perform as the organ of mind, by which 

 we are enabled to hold communion with the ex- 



