PHYSIOLOGY OF THE NERVOUS SYSTEM. 
When to these results, obtained from patho- 
logical researches, we add those of experiment, 
nothing is gained which can be favourable to 
the attribute of sensitive power to the posterior 
columns of the cord. Dr. Baly’s experiments 
on tortoises showed that movements might be 
excited whether the anterior or the posterior 
columns were irritated, much stronger mo- 
tions being excited by the posterior than by 
the anterior columns. Longet found that mo- 
tions might be excited by irritation of the 
terior columns of the cord if the experiment 
d been made immediately after the transverse 
division of the cord, and he refers such mo- 
tions, probably with justice, to an excited state 
of the cord. After a little time this subsides, 
and then M. Longet was able to pass the 
galvanic current through each or both of the 
posterior columns, without exciting any mo- 
tions when the lower segment of the cord was 
acted upon, but causing pain, as evinced by 
loud cries and writhing of the body, when the 
nt segment was tried. From experiments 
of this kind no satisfactory deductions can be 
made: to irritate the posterior columns of the 
spinal cord in a living dog without affecting in 
some degree the posterior roots of the nerves, 
appears to me to be quite impossible, even in 
the hands of the most practised vivisector. 
Neither anatomy, pathological observation, 
nor experiment, lend sufficient countenance to 
the doctrine of the identity of the function of 
the posterior roots and posterior columns to jus- 
tify us in concluding that these columns are the 
ordinary channels for the transmission of the 
sensitive impressions made upon the trunk and 
extremities. 
I have long been strongly impressed with the 
ota that the office of the posterior columns 
of the spinal cord is very different from any 
yet assigned to them. They may be in part 
commissural between the several segments of 
the cord, serving to unite them and harmonize 
them in their various actions, and in part sub- 
servient to the function of the cerebellum in 
regulating and co-ordinating the movements 
necessary for perfect locomotion. 
This view is suggested by a comparison of 
the spinal cord with the brain, and by the ana- 
tomical connections of the posterior columns. 
The brain is an organ composed of various 
segments, which are connected with each other 
by longitudinal commissures. The cord is 
obviously divisible into a number of ganglia, 
each forming a centre of innervation to its 
proper segment of the body. These portions 
must be connected by similar longitudinal 
commissures to those which confessedly exist 
in the brain. If we admit such fibres to be 
necessary to ensure harmony of action between 
the several segments of the encephalon, there 
are as good grounds for supposing their exist- 
ence in the cord as special connecting fibres 
between its various ganglia to secure consen- 
taneousness of action between them. 
The attribute of locomotive power rests upon 
the connection of the posterior columns with 
the cerebellum, and the probable influence of 
that organ over the function of locomotion and 
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the maintenance of the various attitudes and 
postures. Ifthe cerebellum be the regulator of 
these locomotive actions, it seems reasonable to 
suppose that these columns, which are so largely 
connected with it, each forming a large propor- 
tion of the fibrous matter of each crus cerebelli, 
should enjoya similar function, and that, as they 
are the principal medium through which the 
cerebellum is brought into connection with the 
cord, it must be through their constituent fibres 
that the cerebellum exerts its influence on the 
centre of innervation to the lower extremities 
and other parts concerned in the locomotive 
function, and on the nerves distributed to 
these parts. 
The nearly uniform size of the posterior co- 
lumns in the different regions of the cord, 
whilst it may be noted as unfavourable to their 
being viewed as channels of sensation, may be 
adduced as a good argument in favour of their 
being concerned in locomotion and acting as 
commissural fibres. It is a fact worthy of 
notice that these columns experience no marked 
diminution in size until the large sacral nerves, 
which furnish the principal nerves of the lower 
extremities, begin to come off. The reason of 
this is probably because the fibres of these co- 
lumns connect themselves in great part with 
the lumbar swelling of the cord, and some of 
them perhaps pass into the sacral nerves. 
The following remarks will serve to explain 
the manner in which the posterior columns may 
contribute to the exercise of the locomotive 
function. In examining a transverse section of 
the cord in the lumbar region, we observe a 
great predominance of its central grey matter ; 
the posterior columns appear large, and the 
antero-lateral columns seem inadequate in pro- 
portion to the large roots of nerves which 
emerge from it. Now, an analysis of the loco- 
motive actions shows, with great probability, 
that they are partly of a voluntary character, 
and partly dependent on the influence of phy- 
sical impressions upon that segment of the 
cord from which the nerves of the lower extre- 
mities are derived. There are two objects to 
be attained in progression, namely, to support 
the centre of gravity of the body, and to propel 
it onward. The former object is attained by 
physical nervous actions, the latter by mental. 
The support of the centre of gravity of the body 
requires that the muscles of the lower extremi- 
ties, the pillars of support to the trunk, should 
be well contracted in a degree proportioned to 
the weight they have to sustain. The contrac- 
tion of these muscles seems well provided for 
in an arrangement for the developement of 
nervous power by a stimulus propagated to the 
centre, and then reflected upon the motor 
nerves of these muscles. The stimulus is 
afforded by the application of the soles of the 
feet to the ground ; it is therefore proportionate 
to the weight which presses them down- 
wards. It is well known that reflex actions 
are more developed in the lower than in the 
upper extremities, and the surface of the sole 
of the foot is well adapted for the reception of 
sensitive impressions. No object can be as- 
signed for this peculiarity, unless it have re- 
