196 AN AMERICAN TEXT-BOOK OE PHYSIOLOGY. 



Amputation in Man. — When the oerves to a limb have been severed, 

 the consequent changes in the spinal cord depend on the age of the patient at 

 the date of operation, the length of time elapsing between the operation and 

 death, and the level on the limb at which the amputation was made. When 

 the amputation occurs early in life, and the time before death is long, and 

 the level of the amputation high, the alterations are maximum, and consist 

 in an atrophy in the- peripheral efferent nerve-fibres, slight atrophy (or some- 

 times complete disappearance) of the spinal ganglion-cell bodies, atrophy of 

 dorsal root-fibres and their continuations within the cord, and, on the ventral 

 side, disappearance or atrophy of the motor (efferent) cell-bodies in the 

 ventral horn of the cord, together with their axonic outgrowths, the ventral 

 root-fibres, the effect extending outward through the peripheral nerve to the 

 point of section (see Fig. 84). The final appearances are brought about by 

 slow changes, often requiring years for their completion, and hence most of 

 the cases examined tend to show less change than is here described. 1 



Fig. 84.— Cross-section of the spinal cord of the chick, X 100 diameters (van Uehuchten) ; D, dorsal sur- 

 face ; V, ventral surface ; d. r, dorsal root ; v. r, ventral root; g, spinal ganglion. On the left the arrows 

 indicate the direction of the larger number of impulses in the dorsal and ventral roots respectively. 

 The small arrow on the right dorsal root calls attention to the fact that some axones arising in the ven- 

 tral lamina emerge through the dorsal root and convey impulses in the direction indicated. 



The disturbance caused in the two sets of cells is, however, not the same. 

 In the case of the cells of the spinal ganglion, the chief pathway by which 

 they are stimulated under normal conditions is so far mutilated that probably 

 only a small number of impulses passes over them. That some do pass is 

 indicated by the sensations apparently coming from the lost limbs — sensations 

 which are often very vivid and minutely localized. 2 



Thus the cell-bodies located in the spinal cord are to a great degree 

 deprived by such an operation of one principal group of incoming impulses, 

 namely — those which arrive through the dorsal root-fibres that are most 

 closely associated with them ; but at the same time there remain many other 

 ways in which these same cells are normally stimulated. The efferent path- 



1 Marinesco: NeuroL Centralbl., 1892 (reviews the literature); Gregoriew : Zeilschrift /. 

 Heillcunde, 1894, T.d. xv. 



'-' Weir Mitchell : Injuries of Nerves, Philadelphia, 1872. 



