THE NERVOUS SYSTEM AND CONSCIOUSNESS. 737 



ganism. This division is peculiar, because it does not affect nutrition 

 or the ordinary organic processes. In a limb whose nerves are sev- 

 ered there is a loss of sensation ; there is also a loss of movement ; the 

 limb continues to live, but for all limb purposes it might as well be 

 dead. Nerve-matter, therefore, preserves the higher bodily unity. 



In examining this general nerve-function we discover the distinct- 

 ive tasks of fibers and cells. The fibers convey, while the cells origi- 



EiSAitib'a HILUll 



Pig. 5.— Tbaksterbe Section through Human Spinal Cord in Cervical Region, showing the 

 organ to be composed of two eymmetrical halves. (Sappey, after Stilling.) The black portion9 

 correspond to regions containing longitudinal fibers ; the lighter portions represent the cen- 

 tral gray matter and the horizontal roots of nerves ; 5, 6, commissures connecting the sym- 

 metrical halves of the gray matter ; '.1, 11, 11, anterior or motor roots of spinal nerves coming 

 from anterior horna or cornua of gray matter, in which are numerous groups oi^ large ganglion 

 cells ; 13, posterior or sensory roots of spinal nerves, entering the posterior horns of gray mat- 

 ter. Magnified about eight diameters. 



nate, motions. Fibers may convey motions from without inward, or 

 from within outward ; in the former case they are called afferent, 

 in the latter efferent. The nerve-arc is composed of an afferent and 

 an efferent fiber and cell matter. The arrangement of the arc is such 

 that the outer end of the afferent fiber terminates at the surface of 

 the body, the inner end at the cell-matter, while the outer end of the 

 efferent fiber terminates in a muscle, its inner end being also in the 

 same cell-matter. Nothing more than this arc is necessary to pro- 

 duce nerve-action. If an impression be made at the surface of the 

 body, the motion there occasioned is carried by the afferent fiber to 

 the cell-substance ; through this substance the motion is transferred 

 to the efferent fiber, along which it passes to the muscle causing 

 muscular contraction. Since the cell liberates motion, and, being 

 much more unstable than the fiber, liberates motion freely, it often 

 happens that a slight impression at the surface is followed by a very 

 violent contraction of the muscle. 



Our nerve-arc is not a nervous system. "We need only one addi- 

 tional element, however, to form such a system, and this is an ascend- 

 voL. XXVI. — 4*7 



