720y 
the left side.* A longitudinal section of the 
cord along the median line in frogs does not 
cause paralysis; it gives rise, however, to a 
es sae disturbance of the functions of the 
cord which soon subsides.+ 
Continuity of the spinal cord and encepha- 
lon is then the condition necessary to establish 
the control of the former organ over the volun- 
tary movements and sensations of the trunk. 
The disunion of the cord or any portion of it 
from the encephalon dissociates the cord or 
the separated segment of it from all participa- 
tion in mental nervous actions. So long as the 
cord is united with the brain, it takes a certain 
share in mental! nervous actions, in acts of sen- 
sation and volition; this, however, it loses 
when disease or accident separates the one from 
the other. 
It is plain, then, that the spinal cord, although 
apart from the encephalon it takes no share 
in sensations and voluntary actions, (for then, 
indeed, these phenomena cannot take place as 
far as regards the trunk and extremities,) while 
united with the encephalon participates fully 
in sensori-volitional actions, and its integrity 
is quite necessary to the perfection of those 
actions. 
1 repeat that we are not justified in supposing 
that the mind localises itself exclusively in some 
or all of the gangliform bodies, the assemblage 
of which constitutes the encephalon; but this we 
may assert, with perfect justice, that when the 
cord has been separated from the encephalon, 
the mind appears as it were to cling to the 
latter organ, and to lose all its connection with 
the former. 
Does then the cord, under these circum- 
stances, lose all its power? Does it, when sepa- 
rate from the encephalon, shew no indication 
of acting as a nervous centre? Undoubtedly 
it does show abundant indications. A series 
of actions, which had attracted the notice of 
several physiologists, are still capable of being 
developed through the instrumentality of the 
whole cord or of any portion of it, the nerves 
of which may remain uninjured both as to their 
central and peripheral connections. 
Phenomena of this nature may be produced 
in all vertebrate animals. They are, however, 
especially marked in the cold-blooded classes, 
in consequence of the more enduring character 
of the nervous force in those creatures than in 
the warm-blooded. Hence frogs, salamanders, 
snakes, turtles, fishes, have been generally 
selected by physiologists for exhibiting these 
phenomena. In the young of warm-blooded 
animals they are more manifest than in adults 
of the same class. 
If a frog be pithed by dividing the line of 
junction of the medulla oblongata with the 
spinal cord, the following effects may be ob- 
served. After the first disturbance, general 
convulsions, &c., consequent upon the division 
of the cord, the animal, if placed on a table, 
will assume his ordinary position of rest. In 
some cases, however, frequent combined move- 
ments, much resembling acts of volition, will 
* Med. Chir. Trans, vol. i. p. 200. 
+ See Flourens’ Experiments, Syst. Nerveux. 
PHYSIOLOGY OF THE NERVOUS SYSTEM. 
take place for a longer or shorter time after 
the operation. When all such disturbance 
has ceased the animal remains perfectly still — 
and as if in repose, nor does it exhibit the 
slightest appearance or give the least expres- 
sion of pain or suffering. It is quite unable i 
to produce any spontaneous or voluntary move- — 
ment of parts supplied with nerves from be- 
low the section, that is, of the trunk or extre- 
mities. However one may try to frighten it, 
it remains in the same place and posture, — 
The only appearance of voluntary motion is the 
winking of the eyelids, which, however, proba- 
bly is not excited by the will. If, now, a toe be 
pinched, instantly the limb is drawn up, or the 
animal seems to push away the irritating L 
and then draws up the leg again into its old 
position. Sometimes a stimulus of this kind 
excites both legs, and causes them to be thrown 
violently backwards. A similar movement al-~ 
most constantly follows stimulation of the anus. 
If the skin be pinched at any cm some 
neighbouring muscle or muscles will be thrown — 
into action. Irritation of the anterior extre- 
mities will occasion movements of them; but 
it is worthy of note that these movements are 
seldom so energetic as those of the posterior 
extremities. « 
We may remark here, that phenomena ¢ 
this kind are not confined to the trunk M3 
extremities, which are supplied only by spinal 
nerves. The head and face, with which the 
encephalon remains in connection, exhibit 
similar actions. The slightest touch to the 
margin of either eyelid or to the surface of 
the conjunctiva causes instantaneous winking 
the attempt to depress the lower jaw for the 
purpose of opening the mouth is resisted ; a 
the act of deglutition is provoked by applyit 
a mechanical stimulus to the back of the 
throat.* ‘- 
Actions similar to those which take place 
the decapitated frog, occur in the human suk 
when the spinal cord has been separated fi 
its encephalic connections by disease or 
dent. In such cases it is found thatal 
will cannot move the paralysed parts, the lows 
extremities for instance, movements do oce 
~*~ 
em 
¥ 
Dug 
: x 
* Sir Gilbert Blane, in his admirable C 
Lecture on muscular motion, having drawn the 
tinction between instinctive and voluntary action 
makes the following remarks. ‘‘ There are fat 
which show that instinctive actions, even in a 
mals endowed with brain and nerves, do i 
pend on sensation. I took a live kitten, a few di 
old, and divided the spinal marrow by cutti 
across at the neck. The hind paws being then | 
tated by pricking them, and by touching m } 
a hot wire, the muscles belonging to poste 
extremities were thrown into contraction, 80 a 
roduce the motion of shrinking from the inju 
The same effects were observed in another kit 
after the head was entirely separated from 
body.” And again, ‘In an i 
the like phenomena were observable. It 
its knees, when the soles of its feet were tickle 
it performed the act of suction; passed rine @ 
feces ; and swallowed food.” * * * «Thel 
takes place with regard to insects; for, after 
head of a bee is separated from the body, 
hinder part will sting, upon the application of 
a stimulus as would excite the same action in 
animal in a perfect state.” ' 
4 
