158 THE NERVOUS SYSTEM. 



connects the brain with some point on the foot, its length 

 cannot be less than one hundred thousand times greater 

 than its diameter; and yet it performs its work with as 

 much precision as fibres that are comparatively much 

 stronger and less exposed. 



17. The Sympathetic System. The sympathetic 

 system, of nerves remains to be described. It consists of a 

 double chain of ganglia, situated on each side of the 

 spinal column, and extending through the cavities of the 

 trunk, and along the neck into the head. These ganglia 

 are made up for the most part of small collections of gray 

 nerve-cells, and are the nerve-centres of this system. 

 From these, numerous small nerves are derived, which 

 connect the ganglia together, send out branches to the 

 cranial and spinal nerves, and form networks in the vicin- 

 ity of the stomach and other large organs. A considerable 

 portion of them also follows the distribution of the large 

 and small blood-vessels, in which the muscular tunic ap- 

 pears. Branches also ascend into the head, and supply 

 the muscles of the eye and ear, and other organs of sense. 



18. In this manner, the various regions of the body are 

 associated with each other by a nervous apparatus, which 

 is only indirectly connected with the brain and spinal 

 cord; and thus it is arranged that the. most widely sep- 

 arated organs of the body are brought into close and 

 active sympathy with each other, so that, "if one member 

 suffers, all the other members suffer with it." From this 

 fact, the name sympathetic system, or the great sympathetic 

 nerve, has been given to the complicated apparatus we have 

 briefly described. Blushing and pallor are caused by men- 

 tal emotions, as modesty and fear, which produce opposite 

 conditions of the capillaries of the face by means of these 

 sympathetic nerves. 



1 7. The sympathetic system of nerves ? Of what does it consist ? 



18. Association of the various regions of the body ? If one member suffers ? 

 Blushing * 



