THE SPINAL CORD.—GENERAL. 493 
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 matter 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 (hyperesthe- 
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 OF THE SPINAL CORD. 
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, 
these phenomena certainly teach the dependence of one part 
upon another in the normal animal, and should make one cau- 
tious in drawing conclusions from any kind of experiment, in 
regard to the normal functions. As we have often urged in 
