Chapter I: HAD long ago1 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 the structure of each Nerve is similar to that of the Brain.

7. FROM the above Experiments, it appears probable, in the highest degree, that Opium may be absorbed in such quantity as to produce fatal symptoms.

8. THE following circumstances concur in rendering inadmissible an opinion lately proposed by M. FONTANA, that Poisons operate by changes they produce on the mass of Blood, or on some unknown principle connected with the Blood.

a. IF his opinion was just, Poison introduced into a Vein of the extremities, so as to be in contact with this unknown principle, should operate as quickly, and in the same manner as when the Poison is mixed with the Blood near the Heart, which he admits is not the case[4].

b. CUTTING the Spinal Marrow in Frogs, before applying the Poison of the Viper to their Legs, prevents it from killing them[5]; which should not happen, if the Poison acted on the Blood alone.

c. HE acknowledges that an Animal bit in its Leg by a Viper, instantaneously feels acute pain[6]; and it, in like manner, feels instantly great uneasiness when the Poison is mixed with its Blood[7]. We know for certain, that, through the medium of the Nerves, we are instantly rendered sensible of injury done to the most distant parts of our Bodies.

ARE we not, therefore, in the last mentioned Experiment, to conclude, that the uneasiness was produced because the Poison acted upon the Nerves of the Vessels?

d. IN like manner, Animals were convulsed as soon as they were wounded, or received the Poison into a Blood-vessel; and long before the Blood could have reached the Muscles in action[8].

e. AS soon as the distilled Water of Lauro-cerasus was poured into the Stomach of a Pigeon, it was convulsed, died instantly[9], that is, before the Poison could have entered the Mass of Blood.

f. MANY years ago, I found, after cutting the Venæ Cavæ and Aorta of a Frog, that a watery solution of Opium poured into the Heart, occasioned, in a few minutes, convulsions in its Legs; and, after cutting out the Heart, that the Opium poured into the Cavity of the Abdomen affected the Legs in like manner; although, in these Experiments, the Circulation was not only interrupted, but the greater part of the Blood evacuated.

I THEREFORE then concluded[10], and now conclude, that Opium and other Poisons, even after they are mixed with the Mass of Blood, produce their fatal effects, chiefly and almost solely, by acting on the Nerves of the Heart and Vascular System, and, through these, affecting the whole of the Nervous System.

SUMMARY OF EXPERIMENTS MADE ON ANIMALS WITH METALLINE SUBSTANCES.

I SHALL now proceed to state the several circumstances I have observed, in my Experiments, which more directly lead us to judge of the Nature and Cause of Animal Electricity.

1. WHEN two Plates of different Metalline Substances, particularly of Zinc and Gold, between which a living Frog is placed, are brought into contact with each other, those Muscles, which are farther from the Brain and Spinal Marrow than the Metals, are convulsed: and this effect follows, although the Animal and Metals are placed on an inverted glass jar, and that a stick of sealing wax is interposed between the hand of the Operator and the Metals; that is, although the Animal, with the Metals, be insulated.