2IO 



Life and Health 



touch in the fingers to the cerebro-spinal center, which at once 

 hurries off its order along another set of nerves for the hand 

 to drop the hot object. 



f 320. Divisions of the Nervous System. The nervous 

 system consists of two great divisions : the cerebro-spinal 

 system and the sympathetic system. 



The first is the great nerve center of 

 the body, the cerebro-spinal system, which 

 rules the organs of animal life, and 

 includes the brain, the spinal cord, and 

 the cerebro-spinal nerves. 



Nerves are given off from the brain 

 and the cord, and form the mediums of 

 communication between them and the 

 external parts of the body. 



The second division is the sympathetic 

 system. This consists of numerous small 

 nerve centers arranged in oval masses 

 varying greatly in size, called ganglia, 

 or knots. These are either scattered 



(Two nerve fibers, show- , > ,-, -, .-> , , , 



ing the nodes or con- "regularly through the body or arranged 

 strictions of Ranvier in a double chain of knots lying in the 



Tht^utr^het'th fr nt Of the S P ine ' With! the CheSt a " d 



has been dissolved abdomen. From this chain large num- 



SSgT.ffi bers of . nerves are S iven off - which end 

 indicate the nerve chiefly in the organs of digestion, circu- 



FIG. 114. Non- 

 Medullated Fibers. 



^ 321. The Brain as a Whole. The 

 brain is the seat of the intellect, the will, the affections, the 

 emotions, the memory, and sensation. It has also many 

 other and complex functions. In it are established many 

 reflex, automatic, and coordinating centers, which are as inde- 

 pendent of consciousness as are those of the spinal cord. 



