580 



GENERAL PHYSIOLOGY 



kinds of cells, tissues and organs of the cell-community by the 

 central nervous system, the cells of which form in vertebrates the 

 brain and the spinal cord together with the sympathetic nervous 

 system, a central system of administration for the whole cell- 

 community is inaugurated, 

 which from the brain and 

 spinal cord by means of their 

 long paths of conduction 

 brings even most distant 

 parts of the community 

 under a unified control 

 (Fig. 281). Hence the 

 nervous system has been 

 compared very graphically 

 to a telegraphic network, 

 the wires of which put the 

 most distant regions of a 

 country into connection with 

 a central place of govern- 

 ment. The comparison of a 

 central nervous system to 

 a great telegraph station 

 and the nerve-fibres to the 

 telegraph wires is very fit- 

 ting with respect to the 

 principle of centralisation 

 upon which the two are 

 based. But, as has some- 

 times happened, such a 

 comparison ought not to be 

 carried too far ; for example, 

 the nerves should not be 

 regarded simply as conduct- 

 ing-wires for electricity. In 

 reality, nerves are extensions 

 of ganglion-cells, and, like 

 these, consist of living sub- 

 stance, i.e., they have a 

 metabolism with which their 

 life and, therefore, their 

 function are inseparably 

 connected. This follows 

 directly from the fact that 

 the nerve invariably perishes, 



Fm.281.-Ner.vous system of man. The nerve-trunks, ^ any non-nucleated pro- 



which contain centrifugal and centripetal paths of tOplasmiC maSS, alter being 



conduction, pass from the brain and spinal cord to ~, - , ^l," 



all parts of the body, and thus unite the latter Cllt Ott irom tne ganglion- 



* Cel1 t0 



