THE SPINAL COED AS A CONDUCTOR 359 



Hemisection of the cord on one side, as was first pointed out by Brown 

 Sequard, causes the following symptoms : 



(1) Paralysis of the voluntary motor conductors on the same side. 



(2) A paralysis also of the vaso-motor conductors on the same side and, 

 as a consequence, a greater afflux of blood and a higher temperature. There 

 may be some degree of hyperaesthesia on this side. 



(3) There is anaesthesia affecting all kinds of sensibility, excepting the 

 muscular sense, in the opposite side to that of the lesion, owing to the fact 

 that the conductors of sensitive impressions from the trunk and limbs 

 decussate in the spinal cord ; so that an injury in the cervical region of that 

 organ in the right side, for instance, alters or destroys the conductors from 

 the left side of the body. 



(4) There is some degree of anaesthesia also on the side of the lesion, in 

 a very limited zone, above the hyperaesthetic parts, and indicating the level 

 of the lesion in the cord. This anaesthesia is due to the fact that the con- 

 ductors of sensory impressions, reaching the cord through the posterior roots, 

 at the level or a little below the seat of the alteration, have to pass through 

 the altered part to reach the other side of the cord. 



The only direct unbroken cortico-spinal fibres are those contained in the 

 pyramidal tracts. Motor impulses, which start from the cerebral cortex on 

 one side, pass down that side till they react the lower part of the medulla. 

 Here the greater number of the fibres cross over in the pyramidal decussation 

 to run down in the crossed pyramidal tract on the other side of the cord. 

 The few fibres which do not cross over in the pyramidal decussation are 

 continued as the direct or anterior pyramidal tract. These however also 

 cross to the other side in their passage down the cord before becoming con- 

 nected with the anterior cornual cells. Hemisection therefore of the spinal 

 cord in the dorsal region will produce paralysis of voluntary movement and 

 loss of or impaired muscular sensation in the parts supplied by the nerves 

 on the same side below the lesion. 



A great part of the white matter of the cord is concerned then in main- 

 taining connection between the brain and higher parts of the nervous system 

 and the periphery, through the intermediation of the cells of the grey matter 

 of the cord. Corresponding to this function we find a gradual increase in 

 the number of fibres in the white matter as we ascend from the sacral part 

 of the cord to the medulla, the white matter being continually reinforced as 

 it ascends the cord by fibres establishing connection with the ganglion-cells 

 forming the nuclei of the nerve roots. 



Vaso-motor impulses to the limbs travel down the lateral columns of the 

 cord on the same side. 



