THE SPINAL CORD.— GENERAL. 475 



■ways of impulses; though in all instances it is likely that the 

 gray matter of the cord plays an important part in modify- 

 ing them before they reach their destination. Some observers 

 believe that sensory impulses giving rise to pain travel by the 

 gray matter of the cord almost exclusively. It would be easy 

 to lay out the paths of impulses in a more definite and dog- 

 matic manner ; but the evidence does not seem to warrant it, 

 and it is better to avoid making statements that may require 

 serious modification, to say the least, in a few months. The 

 prominent principle to bear in mind seems to be that while 

 there are tracts in the cord of the animals that have been exam- 

 ined and probably of all that have well-formed spinal cords, 

 along which impulses travel more frequently and readily than 

 along others, it is equally true that these paths are not invaria- 

 ble, nor are they precisely the same for all groups of animals. 

 The cord can not be considered independently of the brain ; and 

 there can be no' doubt that the paths of impulses in the former 

 are related to the constitution, anatomical and physiological, of 

 the latter. It is still a matter of dispute whether the cord is 

 itself irritable to a stimulus. As a whole it is without doubt ; 

 as also the white niatter by itself. The gray matter is certainly 

 conducting, but whether irritable or not is still doubtful. Why 

 the sensibility of the side of the body on which one lateral half 

 of the cord has been divided should be increased (Tiyperaesthe- 

 sia), is also undetermined. Possibly it is due to a temporary 

 disturbance of nutrition; or the removal of certain usual inhibi- 

 tory influences from above, either in the cord or brain. 



THE AUTOMATIC FUNCTIONS OP THE SPINAL OORS. 



Reference has been already made to the fact that when por- 

 tions of a mammal's cerebrum are removed the reflexes of the 

 cord become more pronounced, owing apparently to the removal 

 of "influences operating on the cord from higher centers. 



When the cord itself is completely divided across, it often 

 happens (in the dog, for example) that there are rhythmic 

 movements of the posterior extremities — i.e., when the animal 

 has recovered from the shock of the operation — that part of the 

 cord now independent of the rest and of the brain seems to 

 manifest an unusual automatism. The question, however, may 

 be raised as to whether this is a purely automatic effect, or the 

 result of reflex action. But, whichever view be entertained. 



