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 

 briugs even most distant 

 parts of the community 

 under a unified control 

 (Fig. 281). Hence the 

 nervous system has been 

 compared very graphicallj' 

 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, 



Pio. 281.— Nervous system of man. Tho nerve-trunks, 'l^^® ^l^J UOn-nucleated pro- 



which contain centrifugal and centripetal patlis of toplasuiic mjlSS after beinP" 

 conduction, pass from the brain and spinal cord to ^ rr r _li' t 



all parts of the body, and thus unite the latter CUt Oil irom the gaUgllOn- 



through the central nervous system into a luiificd ^„ii j.^ ,.^u;„l^ l^. 'U^l 



whole (After Ranke.) Cell tO whlch it bcloUgS. 



