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                              EXPERIMENTS
                                  ON
                         _THE NERVOUS SYSTEM_,
                 WITH OPIUM AND METALLINE SUBSTANCES;

             MADE CHIEFLY WITH THE VIEW OF DETERMINING THE
                         _NATURE AND EFFECTS_
                                  OF
                          ANIMAL ELECTRICITY.

                       BY ALEXANDER MONRO, M. D.

     PROFESSOR OF MEDICINE, ANATOMY AND SURGERY IN THE UNIVERSITY
       OF EDINBURGH; FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS,
             AND OF THE ROYAL SOCIETY OF EDINBURGH, AND OF
                THE ROYAL ACADEMY OF SURGERY IN PARIS.

                              EDINBURGH:

                  PRINTED BY ADAM NEILL AND COMPANY,
                  FOR BELL & BRADFUTE, AND T. DUNCAN;
                        AND J. JOHNSON, LONDON.

                             M.DCC.XCIII.




                               CONTENTS.

                                                                  _Page_

  INTRODUCTION,                                                        5

  Observations on the Circulating and Nervous Systems of Frogs,        6

  Experiments with Opium,                                              9

  Corollaries from the above Facts and Experiments,                   12

  Summary of Experiments made on Animals with Metalline Substances,   17

  Summary of Facts proved by the foregoing Experiments,               35

  Resemblance of the Fluid put in Motion by the foregoing
  Experiments to the Electrical Fluid,                                38

  The Nervous Fluid or Energy not the same with the Electrical, nor
  with the Fluid put in Motion by the foregoing Experiments,          40

  General Conclusions,                                                42




INTRODUCTION.


WHEN, in November last, I began to make Experiments on Animal
Electricity, of which I read some account to the Royal Society on the
3d of December; I was not only much hurried with business, but could
not procure a sufficient number of Frogs for the purpose. During the
last winter and spring, I prosecuted the subject more fully and with
greater attention; and, on the third day of June, I read a second paper
to the Royal Society, to which I have, since that time, made additions.
I shall now state a summary of the chief circumstances I have observed,
with a few Remarks.




OBSERVATIONS ON THE CIRCULATING AND NERVOUS SYSTEMS OF FROGS.


AS my Experiments with Opium, as well as those on Animal Electricity,
have been performed on Frogs chiefly; I shall premise some observations
on their Circulating and Nervous Systems.

THEIR Heart consists of one Auricle and one Ventricle only, their Aorta
supplying their Air Vesicles or Lungs, as well as all their other
Organs; and, of course, their Venæ Cavæ return the Blood from all
parts to the Heart. The Ventricle of their Heart contracts about sixty
times in a minute; and the purple colour of the Blood which is seen
within it, disappears after each contraction, or the Blood is entirely
expelled by its contraction. For upwards of an hour after cutting out
its Heart, a Frog can crawl or jump; and, for upwards of half an hour
longer, it contracts its Legs when the Toes are hurt, though not with
sufficient force to more its Body from the place where it is laid.

THEIR Encephalon consists of Brain and Cerebellum, each of which, on
its upper part, is divided into two Hemispheres; and, below, they
are conjoined by thick Crura, which form the Medulla Oblongata and
Spinal Marrow, both of which are proportionally larger than in Man,
and more evidently consist of two Cords. There are nine true Vertebræ;
and at the sixth of these, the Spinal Marrow terminates in the Cauda
Equina. The Sciatic Nerves are formed by three pairs of Nerves, sent
out below the seventh, eighth and ninth Vertebræ, and by one pair from
the Os Sacrum. A Nerve, resembling our great Sympathetic Nerve, passes
downwards from the Abdomen into the Pelvis.

TWO days after cutting off the Head of a Frog at its joining with
the first Vertebra, I found it sitting with its Legs drawn up, in
their usual posture; and when its Toes were hurt, it jumped with very
considerable force. Its Heart likewise continued to beat about forty
times in a minute, and so strongly as to empty itself and circulate the
Blood.

IN several Frogs, after cutting off the back part of the six undermost
true Vertebræ, I took out all that part of the Spinal Marrow with the
Cauda Equina which they cover. The lower Extremities were rendered
insensible to common injuries, and lay motionless, yet the Frogs
lived several months thereafter, and the wounded parts of their Backs
cicatrised; and the Bones of their Legs, which I fractured, were
re-united, the Blood circulating freely in their Vessels.

IT is universally known, that if, after amputating the Limb of a warm
blooded Animal, we repeatedly irritate the Nerves which terminate
in Muscles, repeated Convulsions of the Muscles are for some time
produced; and that in Frogs, and other cold blooded Animals, the Nerves
retain this power still longer.

BUT it has been commonly supposed, that, after irritating the Nerve a
given number of times, the effect ceases, Authors conceiving that there
is lodged in the Nerve some fluid, or other energy which is exhausted
by repeated explosions. Instead of this, I have found that the time the
Nerves preserve their power is the same, whether we irritate them or
not; or that their energy is not exhausted by irritation, unless the
irritation be such as sensibly alters their texture.




EXPERIMENTS WITH OPIUM.


I CUT one hole in the fore and upper part of the Cranium and Dura Mater
of a Frog, and another in the back part of the lowermost Vertebræ, and
then injected, from the one hole to the other, a small syringe full
of water, in five ounces of which one ounce of Opium had been infused
for three days. The infusion, by this means brought into contact
with the whole surface of the Encephalon and Spinal Marrow, produced
almost instantly universal convulsions; and, in less than two minutes
thereafter, the Animal was incapable of moving its body from the place
where it was laid. A quarter of an hour thereafter, I found the Heart
beating twenty-five times only in the minute; and so feebly, that it
could not entirely expel the Blood. When, half an hour thereafter,
the Sciatic Nerves were pinched, a light tremor only was excited in
the Muscles of the Leg; and Animal Electricity produced but feeble
twitchings of the Muscles.

THE infusion of Opium, injected in the same manner in Rabbits and in a
Pig, produced similar effects.

I HAD long ago[1] observed, that an infusion of Opium, poured into
the Cavity of the Abdomen of a Frog, after cutting out its Heart,
occasioned, in a few minutes, convulsions of its hind Legs. I have
since found, that, after cutting off the Head, and cutting out the
Heart of a Frog, its hind Legs are considerably weakened by pouring an
infusion of Opium into the Cavity of its Abdomen.

ALTHOUGH an infusion of Opium poured into the Auricle and Ventricle
of the Heart of a Frog, instantly renders that Organ incapable of
contraction, and, even after the Aorta has been previously cut,
occasions convulsions of the Legs, yet I have not found that by Opium
applied to the Brain, the Spinal Marrow, the Heart, or Abdominal
Viscera, the Muscles of the Legs were so entirely killed as not to
perform some motion when their Nerves were pinched, or when they were
acted on by Animal Electricity.

AFTER taking out the lower half of the Spinal Marrow, and likewise
cutting transversely all the parts at the Pelvis, except the Crural
Arteries and Veins and Lymphatics, which probably accompany them, I
found that an infusion of Opium, applied to the Skin and Muscles of
the Legs, affected the superior parts of the Body[2]: more probably,
in my opinion, by absorption, than through any minute remanent
branches of the Nerves, especially as I do not find, on laying the
Vessels so prepared over a gold probe, and touching with it Zinc
laid under the Spine, that convulsions of the Legs can be excited.
At the same time, the quantity of Opium absorbed is so small, that I
could not distinguish its smell or taste in the Blood; nor did I find
these distinguishable, in other Experiments, in which the Frogs were
violently convulsed after applying the infusion to the surface of their
Skin.

ANIMAL Electricity or different metals applied to the Head of a Frog,
or to any part of its Spine above its sixth Vertebra, do not occasion
convulsions of its hind Legs.




COROLLARIES FROM THE ABOVE FACTS AND EXPERIMENTS.


FROM the above Facts and Experiments, it appears,

1. THAT the Frog, after its Head is cut off, feels pain, and, in
consequence of feeling, moves its Body and Limbs.

2. AS the Nerves of the hind Legs are not affected by Animal
Electricity, unless it be applied lower than the fifth Vertebra, these
Nerves do not seem to be derived solely or chiefly from the Brain or
Cerebellum.

3. AS Opium, after the Circulation ceases, affects Organs distant from
those to which it is applied, it is beyond doubt, that the latter
suffer in consequence of Sympathy of Nerves.

4. IT appears that, in this Animal, there is Sympathy of Nerves after
the Head is cut off; or that Sympathy of Nerves does not, in this
Animal, depend entirely on the connection of Nerves within the Head.

5. AS, after cutting off the Head, this Animal is susceptible of pain,
and, in consequence of that, performs voluntary motion, it appears
that, in it, the Brain is not the sole seat of the _Sensorium Commune_.

6. SEVERAL weeks after I had taken out the lowermost half of the Spinal
Marrow, and with it the Cauda Equina, I daily applied, for four days
running, Animal Electricity to the Sciatic Nerves, by passing a gold
Probe between them and the Os Sacrum, and excited several hundreds
of convulsions of the Thighs and Legs, and yet found that, on laying
bare the Femoral Nerves, and pinching them, the Muscles were slightly
convulsed.

HENCE, I apprehend, additional force is given to an opinion I ventured
many years ago to propose[3], that the Nerves do not receive their
energy wholly from the Head and Spinal Marrow, but that the texture of
every branch of a Nerve is such as to furnish it, or that