CHAPTER XXX 



THE SYMPATHETIC NERVOUS SYSTEM 



511. Of what the system consists. The spinal cord con- 

 trols the contraction of the arteries, the peristalsis of the 

 intestine, and the growth of cells. Yet the impulses which 

 it sends out for these purposes pass through another set 

 of nerve cells and nerves called the sympathetic nervous 

 system. 



The sympathetic nervous system consists of small bodies 

 like grains of corn or smaller, called ganglia, from which 

 nerves go out in all directions. There are four main jjairs 

 of ganglia, in the head, and twenty-three in a row down 

 the front of the backbone all connected by nerves. Each 

 ganglion is a collection of nerve cells and nerve fibers 

 bound together by connective tissue. Nerve threads con- 

 nect its cells with the cells of the spinal cord and also with 

 the muscle cells of the arteries and intestine. Through 

 the arteries they probably affect all the cells in the 

 body. The nerve threads are smaller than those of ordi- 

 nary nerves, and seldom form bundles large enough to be 

 seen. They usually consist of a fiber like the central fiber 

 of an ordinary nerve thread .without its fatty covering. 

 They are thus not easily found even with the aid of a 

 microscope. 



The nerves from the ganglia run mainly along the 

 course of the large arteries. Upon the aorta and its 



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