DR. MARSHALL HALL. 
617 
If, on the contrary, we cut off the foot from the left leg, which 
retains the power of motion but no sensation, there is total in- 
sensibility. This experiment is the most surprising of all, and 
affords decided, not uncertain results; because, in the frog, we 
may cut wholly through the roots of the inferior extremities, the 
roots being very few, but thick. These experiments place be- 
yond all doubt the truth of Bell’s doctrine."” 
Reasoning upon this new and valuable discovery. Sir Charles 
Bell observes, It has hitherto been supposed that the office of 
a muscular nerve is only to carry out the mandate of the will, 
and to excite the muscle to action : but this betrays a very inac- 
curate knowledge of the action of the muscular system ; for be- 
fore the muscular system can be controlled under the influence 
of the will, there must be a consciousness or knowledge of the 
condition of the muscle” — whether it be already in a relaxed or 
contracted condition, a state of action or inaction. A limb al- 
ready straightened can in the rectilinear direction be extended 
no further ; for any motion to be given to its component parts, 
the mandate to flex or bend them must be given. Consequently, 
“ To the full operation of the muscular power,” still quoting 
from Sir Charles’s work, “ two distinct filaments of nerves are 
necessary, and that a circle is established between the senso- 
rium and the muscle : one filament or simple nerve carries the 
influence of the will towards the muscle, which nerve has no 
power to convey an impression backwards to the brain ; and 
another nerve connects the muscle with the brain, and, acting as 
a sentient nerve, conveys the impression of the condition of the 
muscle to the mind, but has no operation in a direction outward 
from the brain towards the muscle, and does not, therefore, ex- 
cite the muscle, however irritated.” In the cases on record, in 
which there was an entire loss of sensation, while the muscular 
power was retained, it was necessary for the patients to keep 
their eyes steadily fixed upon any thing they wished to hold in 
their hands, or, from the grasp discontinuing, it would fall to the 
ground. Here, then, is an excellent illustration of “ the con- 
sciousness or knowledge” required for the performance or con- 
tinuance of any muscular action : at the same time that it is an 
instance to shew, that, however distinct the attributes or endow- 
ments of sensation and motion may appear to us to be, they are 
in function indissolubly bound together in the animal economy. 
The condition of the muscle, then, being made known by the 
sentient nerve to the brain, or nervous centre, an influence is 
reflected along the motor nerve, which occasions the contraction 
of the muscle ; thus “ establishing a circle” of nervous action or 
influence u between the sensorium and the muscle 
4 M 
VOL. x i v . 
