CHAPTER IX 



THE NERVOUS SYSTEM 



The nervous system may be compared to the tele- 

 phone system of a large community the brain repre- 

 senting the central office, where calls are answered and 

 connections made; the spinal cord corresponding to the 

 large cables conducting the mass of wires to and from 

 the office, the peripheral nerves to the wires of the in- 

 dividual subscribers. The analogy is, of course, imper- 

 fect, but serves the same purpose as a diagrammatic 

 drawing. Nerves carrying impulses from the periphery 

 to center are like wires running from individual to cen- 

 tral ; while those which run to muscles, glands, etc., 

 would resemble wires running to the individuals called, 

 after the connection has been made central in this in- 

 stance resembling the function of a nerve cell in a re- 

 flex arc in its simplest form i.e., an afferent nerve pass- 

 ing to a cell and an efferent nerve from another con- 

 nected cell to periphery. Such an arc w^ould be com- 

 plete if we conceive of an organism possessed of a skin 

 with a sensory nerve, a muscle to move the organism, a 

 nerve cell to respond to an appeal from the surface and 

 a nerve fiber from cell to muscle. If we imagine that 

 such an organism encounters something painful, the 

 course of the nerve impulse would be from the nerve 

 ending in the skin to the cell, where the danger is rec- 

 ognized and an order sent along the efferent nerve to 

 the muscle to contract and remove the organism from 

 daner. 



