FUNCTIONS OF THE SPINAL CORD. 393 



portion, including the whole thickness, of the spinal cord. 

 Such lesions destroy the communication between the brain and 

 all parts of the spinal cord below the seat of injury, and con- 

 sequently cut off from their connection with the mind the 

 various organs supplied with nerves issuing from those parts of 

 the cord. But if this lower portion of the cord preserves its 

 integrity, the various parts of the body supplied with nerves 

 from it, though cut off from the brain, will nevertheless be sub- 

 ject to the influence of the cord, and, as presently to be shown, 

 will indicate its other powers as a nervous centre. 



From what has been already said, it will appear probable 

 that the conduction of impressions along the cord is effected 

 (at least, for the most part) through the gray substance, i. e., 

 through the nerve-corpuscles and filaments connecting them. 

 But there is reason to believe that all parts of the cord are 

 not alike able to conduct all impressions; and that, rather, as 

 there are separate nerve-fibres for motor and for sensitive im- 

 pressions, so in the cord, separate and determinate parts serve 

 to conduct always the same kind of impression. 



The important and philosophical labors of Dr. Brown-Sequard 

 have cast much new light on all relating to the functions of 

 the spinal cord. It is not possible to do justice to these inves- 

 tigations in any summary, however lengthy and complete: the 

 whole series (delivered in lectures at the College of Surgeons) 

 must be read and studied. An attempt will be made here to 

 point out only the principal conclusions deducible from them. 



a. Sensitive impressions, conveyed to the spinal cord by root- 

 fibres of the posterior nerves are not conducted to the brain by 

 the posterior columns of the cord, as hitherto has been gener- 

 ally supposed, but pass through them into the central gray 

 substance, by which thev are transmitted to the brain (Fig. 

 142). 



6. The impressions thus conveyed to the gray substance do 

 not pass up to the brain along that half of the cord correspond- 

 ing to the side from which they have been received, but, almost 

 immediately after entering the cord, cross over to the other side, 

 and along it are transmitted to the brain. There is thus, in 

 the cord itself, a complete decussation of sensitive impressions 

 brought to it; so that division or disease of one posterior half 

 of the cord is followed by lost sensation, not in parts on the 

 corresponding, but in those of the opposite side of the body. 



c. The various sensations of touch, pain, temperature, and 

 muscular contraction, are probably conducted along separate 

 and distinct sets of fibres. All, however, with the exception 

 of the last named, undergo decussation in the spinal cord, and 

 along it are transmitted to the brain by the gray matter. 



