AND OF THE SYMPATHETIC NERVE. 165 



bodies of the vertebree. It is in constant communication 

 with the spinal nerves, consequently, when other nerves are 

 potent, the sympathetic may be present. 



Of nerves. — Nerves are white glistening threads, every 

 where to be found throughout the body. Nerves are of 

 three kinds, motor, sentient, and special. A motor nerve 

 conveys motion only, and is incapable of feeling. A sen- 

 tient nerve transmits sensation to the brain, and is incapa- 

 ble of conveying motion from it. A special nerve endows a 

 part with one sense, and one sense only. It may go to the 

 eye for sight, as the optics do, but, if compressed or pinched, 

 they feel no pain, and are incapable of motion ; the organ 

 then appears to emit a flash of light ; thus, people speak of 

 their eyes flashing fire, when they run against any thing in 

 the dark. The four orders of nerves rule the body. The 

 sentient render us cognizant of pain ; the motor make the 

 limbs move in obedience to the will ; and the special endow 

 certain parts with particular faculties ; while the sympathetic 

 nerve, over which the brain can exercise no control, regu- 

 lates all the functions which go on continually without our 

 knowledge, but are essential to the prolongation of life. 



Structure of nerves. — Nerves are composed of very minute 

 filaments, bound up in a sheath of pia mater, or cellular 

 tissue, called neurilema. They receive nmch blood in pro- 

 portion to their size ; though they never become red. Hence 

 we may infer the importance of the blood, since it is sent 

 to nerves ; but no nerves are sent to the blood, though 

 many may be distributed to the tubes by which the blood 

 is conveyed. A nerve never terminates ; it passes around a 

 part, and joins another sheath, but it does not appear to 

 end. When cut, nerves have the power of reunion ; even 

 though a piece be taken away. It is disputed whether true 

 nervous filaments are reproduced ; but something is formed 

 which answers their purpose, since by it is carried on all 

 their functions. There is no immediate physiology attached 

 to the brain, or to nerves, worthy of being inserted in this 

 place. Books are written on such subjects ; but all they 

 assert beyond first principles is open to objection, if not to 

 decided refutation. Special nerves terminate in fine bulbous 

 extremities ; and though we have spoken of pure motor and 



