620 THE EXCITO-MOTORY NERVOUS SYSTEM OF 
upper part of the medulla oblongata was now destroyed by an 
instrument passed through the orifice made by the poll-axe: there 
were violent convulsions ; the respiration ceased, and the eyelid 
and eyeball remained motionless on the application of stimuli. 
“The blow with the poll-axe annihilated the cerebral or senti- 
ent and voluntary functions, and a peculiar set of excito-motory 
phenomena remained. Deep lacerations produced no evidence 
of the former ; the touch of a straw induced a full manifestation 
of the latter. The destruction of the medulla oblongata removed 
all trace of excito-motory phenomena in the eyelid and eyeball.” 
Here, as in the case of the frog, the distinction between such 
functions as originate from the cerebrum and such as belong to 
the spinal marrow— of which the medulla oblongata is a prolon- 
gation — became evident; it was also manifest — as Sir C. Bell 
had proved before — that the continuance of respiration depended 
upon the medulla oblongata ; and could the spinal marrow have 
been destroyed, no doubt the same results would have been 
obtained, demonstrating the remnant of vitality — irritability . 
Moreover, there is an important conclusion likewise deducible 
from these and like experiments — that although vitality may be 
removed as it were, and for a time maintained in the headless 
trunk, yet that this life even — which may be regarded as purely 
organic — cannot be continued in the absence of the brain. Indeed, 
not only is it in nature impossible for one part of the same — the 
nervous — system to subsist without the other, but equally impos- 
sible is it for any one complete system to continue in action with- 
out support from others of the body. Of the different systems 
of which the animal economy is composed — the nervous, the cir- 
culatory, the respiratory, the digestive, &c. — every one is reci- 
procally dependent, and all are essential to the maintenance of 
life and health. 
It has been seen that, even after decapitation, if the spinal 
marrow be exposed, and any part of it stimulated, the muscles 
to which the nerves coming off below the stimulated part are 
distributed are excited to contraction : the same effect is also 
produced by stimulating the nerves themselves. The agent or 
principle of action, which in this case evidently originates in the 
spinal marrow, or even in the nerve itself, being said — and in- 
deed having been proved to be — the same incomprehensible in- 
fluence which Haller called the vis nervosa ; and which here 
manifests its action in a direct line or manner from the marrow 
or nervous centre to the extremity of the motor nerve. Nor was 
it known, or at least not demonstrated, until taught and illus- 
trated by Dr. M. Hall, — that this same vis nervosa was, inde- 
pendently, capable of acting in a retrograde course ; that it was 
