FUNCTIONS OF THE SPINAL CORD. 



629 



FIG. 233. 



lateral columns be divided, all power on the side of the section is lost. 

 [Dr. Worooc.hiloff in experimenting on rabbits by dividing the cord at the 

 last dorsal vertebra, arrived at the conclusion that 

 all the channels of motor and sensory impressions 

 are in the lateral columns. 1 ] Some diminution, 

 though not entire abolition of voluntary control 

 over the movements of the posterior extremities of 

 the same side is caused by division of the posterior 

 columns and gray substance ; the reason of this re- 

 sult is clear from an examination of Fig. 233. It 

 is here seen that the section of the antero-lateral 

 column (a, b) divides all the fibres connecting the 

 motor cells in the anterior horns of the gray sub- 

 stance with the brain ; whilst section of the gray 

 substance and posterior columns (c, d} only destroys 

 a certain number of the cells and their communica- 

 tions with the brain, those above and below remain- 

 ing uninjured, and therefore retaining their activity. 

 The section of one antero-lateral column does not produce quite complete 

 paralysis of the parts on the same side supplied by nerves issuing from the 

 cord behind the section, and it would seem probable that some of the motor 

 fibres run in the anterior parts of the gray substance. 



The Gray Substance of the Spinal Cord. The gray substance of the cord is 

 undoubtedly the channel through which most sensory impressions are con- 

 ducted to the brain, and in it are contained at different levels those groups 

 of ganglionic cells or nerve-centres, which preside over certain special func- 

 tions. It is remarkable that it does not respond to direct stimulation, and 

 that, notwithstanding that it contains so many sensory fibres, it may be 

 pricked, pinched, or otherwise irritated, without any indications of pain 

 being given by the animal. This peculiarity, first pointed out by V. Deen, 

 has led Schiff to apply the term resthesodic 2 to it, and he believes that it is 

 capable of conducting in any direction either transversely or longitudinally. 

 That sensory impressions are chiefly con- 

 ducted through the gray substance, is shown 

 the one hand by retaining it intact, 



FIG. 234. 



on 



so 

 CA 



FIG. 235. 



whilst all the white columns are divided 

 (Fig. 234), when the sensibility of the hind 

 limbs will be found to be but slightly im- 

 paired ; and on the other hand by dividing the gray substance alone (Fig. 

 235), when the sensitiveness of the posterior extrem- 

 ities will be found to be entirely lost. But it can 

 be further shown by experiment, that the sensory 

 fibres of the posterior roots of the spinal nerve do 

 not ascend on their own side, but cross over to the 

 opposite side, either immediately, or after a short as- 

 cending or descending course. Thus, if a series of 

 sections be carried from without inwards, the first 

 of which divides the cord as far as to the imaginary 

 line A, Fig. 235, and the succeeding cuts be made 

 progressively deeper and deeper as to B, c, D, and E, 

 it will be found on testing the sensibility of the ani- 



.A. c 



1 [Recent Report in Physiology, hy H P. Bowditcli, M.D., Ludwig's 



2 From aiaOrjaic, sensation, and odor, a path. Op. c'it., p. 247. 



Arbeiten, 74.] 



