77/A' XERVOUS SYSTEM 229 



variety, or, in other words, the nerve-fibres ; the same as we 

 have observed forming a part of the brain. But the nerves, 

 instead of being soft and pulpy, as in the case of the brain, 

 are dense in structure, being hardened and strengthened by 

 means of a fibrous tissue which surrounds each of these deli- 

 cate fibres, and binds them together in glistening, silvery 

 bundles. Delicate and minutely fine as are these nerve-fibres, 



FIG. 54>. SECTION OF SPINAL CORD, WITH ROOTS OF SPINAL NERVES. FRONT VIEW 



it is probable that each of them pursues an unbroken, isolated 

 course, from its origin, in the brain or elsewhere, to that par- 

 ticular point which it is intended to serve. For, although their 

 extremities are often only a hair's breadth distant from each 

 other, the impression which any one of them communicates is 

 perfectly distinct, and is referred to the exact point whence 

 it came. 



19. This may be illustrated in a simple manner, thus : if two 

 fingers be pressed closely together, and the point of a pin be 

 carried lightly across from one to the other, the eyes may be 

 closed, and yet we can easily note the precise instant when 

 the pin passes from one finger to the other. If the nerve- 

 fibres were less independent, and if it were necessary that they 

 should blend with and support each other, all accuracy of 

 perception would be lost, and all information thus afforded 

 would be pointless and confused. These silvery threads must, 

 therefore, be spun out with an infinite degree of nicety. Imag- 

 ine, for instance, the fibre which connects the brain with some 



19. How may we illustrate the fact ? The fibre connecting the brain with a point in the 

 foot? 



