THE SPINAL CORD.—GENERAL. 497 
more must it be true of different groups of animals, the habits 
of which differ so widely! Experiment has proved this also so 
far as it has gone; hence the great danger of laying down laws 
for the spinal cord from the investigation of one animal or 
even one group. Recent investigations have shown that, in 
persons crippled from birth, or for long periods, reflexes which 
had never been properly established may, as the result of opera- 
tive procedure, become possible through training. It has also 
been shown, both by experiment and clinical experience of the 
kind referred to, that when certain reflexes are imperfectly de- 
veloped others are also defective, again impressing the im- 
portance of that balance of development which is essential to 
health or the normal condition of an animal. This subject is 
very wide, of great practical importance, and deserves consider- 
ation beyond what our limits of space will allow. 
All the facts go to show that the cord is made up of nervous 
mechanisms—if we may so speak—which are naturally associ- 
ated, both structurally and functionally, with certain nerves 
and muscles; these, like the paths which impulses take to and 
from the brain, though usual, are not absolutely fixed, though 
more so as reflex than conducting paths, while they are con- 
stantly liable to be modified in action by the condition of 
neighboring groups of mechanisms, etc. 
We have said less about the gray matter of the cord asa 
conductor than its importance perhaps deserves. It is believed 
by many that impulses which give rise to sensations of pain 
always travel by the gray matter; and there is not a little evi- 
dence to show that, when none of the white columns are avail- 
able owing to operative procedure, disease, or other disabling 
cause, the gray matter will conduct impulses that usually pro- 
ceed by other tracts. 
Synoptical.—The spinal cord is composed of large ganglionic 
nerve-cells, fibers, and connecting neuroglia., Functionally it 
is a conductor, the seat of certain automatic centers and of 
reflex mechanisms. Probably in every case the one function is 
to a certain extent associated with the other—i. e., when the 
cord acts reflexly it is also a conductor, and the cells concerned 
are so readily excited to certain discharges of nervous energy 
that automaticity is suggested, and so in other instances: thus, 
in the case of automaticity, reflex influence or afferent impulses 
are with difficulty entirely excluded from consideration. 
The great majority of conducting fibers seem to cross either 
in the cord itself or in the medulla oblongata. The conducting 
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