Experimental Researches applied to Physiology and Pathology.
By E. Brown-SeQUARD, M. D., of Paris.
(Continued.)
XXI.--ON MUSCULAR IRRITABILITY IN PARALYZED LIMBS, AND ITS
SEMEIOLOGICAL VALUE.
Marshall Hall has published many papers, in which he has tried to
prove that the degree of muscular irritability in paralyzed parts maybe
used as a means of diagnosis between cerebral and spinal paralysis.
He calls cerebral paralysis that in which the paralyzed part is de-
prived of the action of the brain, but not entirely, or not in the least, of
the influence of the spinal cord. On the contrary, he calls spinal
paralysis that in which the palsied part is altogether deprived of
the action of both the brain and the spinal marrow. The cause
of the cerebral- paralysis may be seated either in the encephalon or
the spinal cord; and thecause of the spinal paralysis may be seated
either in the spinal cord or in the nerves.
In the same individual these two kinds of paralysis may exist
together. Suppose a man in whom the brachial enlargement of
the spinal cord is considerably softened, and consequently unable
to act; the upper limbs then have a spinal paralysis, and the
lower limbs, receiving their nerves from a healthy part of the spinal
cord, have only a cerebral paralysis.
According to Marshall Hall, the cerebral paralysis is attended by
augmented muscular irritability, and the spinal paralysis is attended
by diminished irritability. He bases this opinion on the following
experiments, and on some clinical observations.
On six frogs he divided the spinal marrow immediately below
the origin of the brachial nerves ; and he removed a portion of the
ischiatic nerve of the right posterior extremity. He had imme-
diately, or more remotely, the following interesting phenomena :
1st. The anterior extremities alone were moved spontaneously ;
both posterior extremities remaining entirely motionless when the
animal, placed on its back, made ineffectual efforts to turn on the
abdomen.
2d. Although perfectly paralytic in regard to spontaneous motion,
the left posterior extremity, that still in connexion with the spinal
marrow, moved very energetically when stimulated by pinching the
toes with the forceps.
3d. The right posterior extremity, or that of which the ischiatic
neive was divided, was entirely paralytic, both in reference to spon-
taneous and excited motions.
4th. After the lapse of several weeks, whilst the muscular irri-
tability of the left posterior extremity was gradually augmented, that
of the right was gradually diminished,—phenomena observed when
the animal was placed in water through which a slight galvanic
shock was passed accurately in the direction of the mesial plane.
5th. Strychnine being now administered, the anterior extremities
and the left posterior extremity, or that still in connexion with the
spinal marrow, became affected with tetanus; but the right poste-
rior extremity, or that severed from all nervous connexion with the
spinal marrow, remained perfectly placid.
6th. Lastly, the difference in the degree of irritability in the mus-
cular fibre of the two limbs was observed, when these were entirely
separated from the rest of the animal.
After this exposition of the results of his experiments, Marshall
Hall adds : “ In a word, the muscles of the limb paralyzed by its
separation from both cerebrum and spinal marrow, had lost their
irritability ; whilst those of the limb separated from its connexion
with the cerebrum only, but left in connexion with the spinal mar-
row, not only retained their irritability, but probably possessed it in
an augmented degree.*
* On the diseases and derangements of the nervous system. 1841, p.
215.
It is easy to prove that Marshall Hall has been completely mis-
led by his experiments.
It is well known that the more a muscle is excited, the more it
contracts. As the degree of irritability is judged by the degree of
the contraction, it follows that to know what is the degree of mus-
cular irritability we ought to apply the same excitation to the mus-
cles we desire to compare. In his experiments with galvanism and
with strychnine, Marshall Hall has not done so. He has applied
galvanism, so as to excite much more the muscles of the left side
united with the spinal cord, than those of the right side.
The muscles of the left side were excited :
1st. Directly by the galvanic current.
2d. In consequence of the excitation of the motor nerves.
3d. In consequence of the excitation of the spinal cord, directly
by the galvanic current, and secondarily in consequence of the
excitation of the sensitive nerves.
So that the muscles on that side were moved not only by the
direct excitation on them, but also by a reflex action, and in conse-
quence of the direct excitation of the spinal cord.
As to the muscles of the right side, they were only excited by
the small part of the galvanic current passing in them. During the
first, and perhaps the second and the third week after the section of
the ischiatic nerve, the muscles were also slightly excited by the
motor fibres of that nerve, but after that time these fibres had lost
their vital property, and were unable to excite a contraction in
muscles.
From this analysis it results clearly that the mode of comparison
of the two limbs, by the passage of a galvanic current, as it has
been employed by Marshall Hall, could not decide in which side
the muscles were more irritable.
The use of strychnine, also, could decide nothing in this ques-
tion, because, as I have proved in a former article, this poison is not
able to act upon muscles. It acts only on the nervous centres, and
especially on the spinal cord. Therefore, the production of tetanus
in one limb and not in the other, in the experiment of Marshall
Hall, proves nothing at all as to the degree of muscular irritability.
To know what is that degree, it is necessary to separate the two
limbs from the trunk, and then to excite directly the muscles. Mar-
shall Hall has made this experiment, but he says nothing about the
circumstances under which it was performed, and these circum-
stances were, as it will be shown, extremely important.
In my experiments, instead of dividing only the ischiatic nerve,
I divided the four nerves going to one of the posterior limbs, of
many frogs, in whom the spinal cord was divided immediately
behind the roots of the brachial nerves.
I have found on the separated limbs of these frogs :
1st. That, at first, the muscular irritability was greater in the
limb which had been deprived of the action of the spinal cord and
of the brain, than in the limb deprived only of the action of the
brain.
2d. That, at a variable time after the operation, the irritability
was at the same degree in the two limbs.
3d. That, at last, the irritability became greater in the limb only-
deprived of the action of the brain, than in the other.*
* There is, in these experiments, a cause of error, arising from the
existence on one side, and the absence, or, at least, a diminution in the
other, of the vital power of the motor nerves ; but the difference is trifling
when the nerves are divided very near their entrance in the muscles.
The differences in the degree of irritability have been
observed : 1st. By the degree of the contraction under the influence
of the same excitation; 2d. By the duration of irritability.
I have found that during a time, varying much according to sea-
sons, and to many other circumstances, the muscular irritability
increases in the two posterior limbs in a frog operated upon as I
have described, and that the increase was more considerable in the
limb where the nerves were divided than in the other.
If we compare two frogs, one operated on as before, and another
having only had a division of all the nerves on one of the pos-
terior limbs, we find, a few days after the operation, that in the
four limbs separated from the body there are great differences as
to the degree and the duration of muscular irritability: 1st. The
three paralized limbs have a greater irritability than the one not
at all paralyzed. From the three paralyzed limbs the two in
which the nerves have been divided have both the same degree
of irritability, and more than the limb in which there was only
what Marshall Hall calls a cerebral paralysis. 2d. The irrita-
bility has lasted longer in the two limbs in which the nerves had
been cut, than in the two other limbs ; and from these two, that
in which there was a cerebral paralysis has remained longer
irritable.
If wo examine the irritability in the posterior limbs of two
frogs, operated on as aforesaid, for ten, twelve, or fifteen days,
then we find that it is nearly at the same degree in the three
paralyzed limbs, and greater there than in the non-paralyzed
limb.
If the comparison is made four or five weeks after the opera-
tion, then the non-paralyzed limb has a greater irritability than
the three paralyzed, and, from these three, the one deprived only
of the cerebral action has a greater irritability than the two
others.
The same experiments made on other animals than frogs, i. e.
on guinea-pigs and rabbits, have given like results. I shall pub-
lish the details of these last experiments in a special paper, in
which I intend to examine the value of the clinical observations
of Marshall Hall, R. B. Todd, Duchenne de Boulogne, and
others. I will merely state here, that in many cases it is almost
impossible to know what is the difference in the degree of mus-
cular irritability in a paralyzed limb, compared with a healthy
limb, in a living man or animal. Galvanism and strychnine can-
not give us any exact notion in this respect. I ought to add,
that if we could know what is the relative degree of irritability
in a paralyzed limb, we could not make use of that knowledge
for the diagnosis of the seat of the alteration producing the
paralysis. On the other side, we do not want to know what is
the degree of irritability in order to establish such a diagnosis.
It will be, almost constantly, easy to know whether a paralysis is
a cerebral or a spinal one. The existence of reflex actions in
the paralyzed parts, is sufficient to prove that there is a cerebral
paralysis, and the absence or the slight degree of these actions
will prove that there is a spinal paralysis.
The following conclusions may be drawn from the facts
above related, and from others that I have not yet published.
1st. The degree of muscular irritability in paralyzed parts,
becomes rapidly greater than in the healthy parts, but, after a
variable length of time, it diminishes, and, as it is well known,
it may disappear.
2d. The muscles deprived of the action of both the brain and
the spinal marrow, become rapidly more irritable than the mus-
cles deprived only of the action of the brain, but, after a certain
time, there is also in them a more rapid diminution of irritability
than in the others.
3d. It appears certain that the muscular irritability never
disappears completely in parts deprived only of the cerebral
action.*
* I have had a pigeon on which nearly an inch of the costal part of the
spinal cord had been removed, and on which the muscular irritability in
the posterior limbs, and a very great reflex power, have existed as long as
I have taken care of it, i. e. more than twenty-seven months. I ought to
say that there has been no re-union of the separated parts of the spinal
cord.
4th. In certain cases of paralysis, and more particularly of
the face, as after the removal of a large part of the facial nerve,
the muscular irritability may exist for years, at least in rabbits
and other animals.
Sth. It is very difficult, and sometimes almost impossible, to
know the relative degree of muscular irritability in healthy parts
compared with paralyzed parts, and such a knowledge could not
be of a great semeiological value.
6th. The existence or the absence of reflex actions as a means
of diagnosis between the cerebral and the spinal paralysis, has
a much greater value than the degree of muscular irrita-
bility.
(To be continued.)