CH. XLV.] SECTION OF THE SPINAL COKD 659 



spinal cord always takes place in an upward direction, but Sher- 

 rington in his work found many exceptions to this rule, and he 

 sought for the paths which are capable of carrying the impulses 

 down the cord by a very ingenious method. The spinal cord of a 

 dog was completely divided across, and the animal was kept alive 

 for a considerable time afterwards; sufficient time was allowed to 

 elapse (roughly about a year) for all traces of the degeneration due 

 to this lesion to have disappeared. The cord is then left, as it were, 

 like a cleaned slate, on which once more a new degeneration can be 

 written without fear of confusion with a previous one. The second 

 degeneration produced by such an operation as hemisection would 

 then affect the intra-spinal fibres only, all the long tracts from brain 

 to cord having been wiped out by the first operation. The complete 

 topography of all these fibres, which are very numerous, has not yet 

 been worked out. The degenerated fibres are scattered throughout 

 the white matter, but are most numerous at the margins of the cord. 

 This is especially true for the longer fibres, and some of them appear 

 to be very long indeed. In the case of the longer fibres there is no 

 evidence of decussation; in the case of the shorter fibres there is 

 some evidence that they in part cross to the other side. 



Section of the Spinal Cord. 



Complete transverse section of the spinal cord leads to : 



1. Loss of motion of the parts supplied by the nerves below the 

 section on both sides of the body. The paralysis is not confined to 

 the voluntary muscles, but includes the muscular fibres of the 

 blood-vessels and viscera. Hence there is fall of blood-pressure, 

 paralysis of sphincters, etc., immediately after the operation, but 

 there is considerable recovery of involuntary muscles, as they are 

 supplied by autonomic nerves ; any voluntary control over the 

 sphincters is, however, permanently lost. 



2. Loss of sensation in the same regions. 



3. Degeneration, ascending and descending, on both sides of the 

 cord. 



Complete transverse section of the spinal cord may produce 

 immediate death if the operation is performed sufficiently high in 

 the cervical region; for the paralysed muscles will then include 

 those of respiration. The spinal cells from which the phrenic and 

 other respiratory nerves originate are then cut off from the respir- 

 atory centre in the bulb above them, and the animal will die of 

 asphyxia. One sees the same thing after severe injury to the upper 

 cervical cord in man, as when he " breaks his neck." 



Hemisection. If the operation performed is not a complete cut- 

 ting of the spinal cord across transversely, but a cutting of half the 

 cord across, it is termed hemisection, or semi-section. This loads to : 



