CHAPTER XXVIII 



NERVES 



477. Uniformity of cell action. Certain cells forming 

 the nervous system are set apart for purpose of command- 

 ing the rest to work in the proper time and manner. The 

 commanding cells, called nerve cells, form the essential 

 part of the brain and spinal cord. From them as a center, 

 fine threads called nerves run to the cells of the body. 

 The outer end of each nerve thread touches a company of 

 cells and carries to them the orders from the central nerve 

 cells. Although each cell in the body lives and acts inde- 

 pendently of the rest, yet the central nerve cells cause all 

 to act in harmony. 



478. Nerves. Each nerve thread is composed of a 

 central fiber surrounded by a protective layer of a kind 



of fat. The whole 

 thread is only about 

 A * n inch in diam- 



A nerve thread (X 400). ' . 



eter. Those which 



a central conducting fiber. b covering of fat. 



go to each part of 



the body, as a hand or leg, run together in a bundle, which 

 divides into its separate threads upon reaching its destined 

 part. Each bundle of nerve threads is usually called a 

 nerve. The main nerves of the arms are about the size 

 of knitting needles, while the great sciatic nerve of the 

 leg is as large as the end of the little finger. 



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