352 HITCHCOCK'S ANATOMY 



641. Use of Spinal Nerves, — The use of the Spinal 



Nerves is to convey impressions made at the surface of the 

 body— including the extremities — to the brain, and to trans- 

 mit impulses to the muscles from the brain. Both of these 

 influences are transmitted by the same nerve or filament,, 

 though in opposite directions. From carefully conducted ex- 

 periments it seems quite probable that the " coarse fibers' ' 

 transmit the impulses to the muscles, and are called afferent, 

 while the fine fibers conduct the impressions to the brain, and 

 are called efferent. And in the muscular nerves the coarse 

 fiber is proportioned to the fine as 10 : 3.3, while in the 

 trunk, as it issues from the spinal cord, it is in the ratio of 

 10 : 11. 



HYGIENIC INFERENCES, 



642. The Nervous System not easily Diseased. — 1. It 

 is a singular fact that the nervous system, so delicate in its 

 organization and mysterious in many of its functions, is to 

 so small an extent dependent upon any particular rules for 

 the maintenance of its health, the main thing necessary for 

 its welfare being an attendance to the general health of the 

 body. 



643. It needs Action. — 2. The nervous system, like all 

 other parts of the body, requires action for its health. If a 

 person has nothing upon which he can exert his nervous 

 energy, he is liable to disease ; and no class of people are so 

 subject to nervous diseases as the wealthy, who are obliged to 

 make little exertion to procure the necessaries and luxuries of 

 life. Hence we infer that employment of some kind is indis- 

 pensable to the health of the nervous system. 



644. Sleep indispensable to its Health.— 3. This system 



641. What is the use of the spinal nerves? What is the difference in function between 

 the coarse and the fine fibers? 642. Is the nervous system easily ufl>cted by serious dis- 

 ease ? 643. What is the necessity of action to the nervous system ? 



