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of my pushing the sucker, owing to its not being exactly fitted to the sides of the syringe: I observed to the persons present, that the experiment had failed, but was surprised to hear in 'reply, that the animal was dead. I do not think ten seconds passed betwixt the time of the liquor's flowing back, and the death of the animal, which had actually taken place. I cannot estimate the quantity of poison introduced into the blood, but as the animal died, fome must necessarily have found its way thither; had not this happened, I should have supposed, from the quantity which flowed back into the tube, that not a single drop of it had entered the jugular vein.

Having put my syringe in better order, I introduced, says he, two-drops of water, with which I had previously mixed about a quarter of a drop of the aqueous solution of the poison I have spoken of. I scarcely began to inject this liquor by the jugular, when the rabbit fell, without motion and without life, as if struck by lightning. I do not think half a drop was introduced.

The death of these animals was more sudden than in the cases of introducing in a funilar way the venom of the viper into the blood; and the whole body was more funk and relaxed, the limbs being rendered as pliant as in animals that have been dead a long time. In animals

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bit by the viper, the blood is often coagulated in the vessels, and partly fuid ; in those destroyed by the ticunas it is always fluid. As the coagulability of the blood is governed by the same laws as the irritability of the fibre *, this is what we might expect; and we find also, that the venom of the viper cannot overcome the irritability of cold blooded animals, whereas the poison of the ticunas is fatal to almost every species of animal t. The muscles of the animals who are killed by the ticunas appear reinarkably pale. The blood in the venous vessels near the heart is darker than usual, and not coagulated. The abdominal viscera is not fenfibly changed. But I observed, says FONTANA, a great change in the lungs, a vifcus very effential to life. I generally found it more or less spotted; the spots were frequently very large and lvid.

This change in fo noble an organ deferves the utmost attention.' It was nearly the same with respect to the

* Vide page 353, line 3. * + Except the viper and adder, which are peculiarly tenacious of life. Adders and vipers may be cut into pieces, and so tenacious are they of life, that each part will remain for a long while irritable. This principle is so predominant in their nature, that few poisons are able to overcome it. Some adders, upon the application of the ticunas, seemed indeed, however, less lively than usual, and the hinder part of the body, which was wounded, became benumbed, and lost its natural motion in a sensible degree, and that for several hours; but none died from this poison.----FONTANA.

venoın of the viper *. The air within the cells was very visible through the external membrane, when examined with a microscope ; and upon a puncture being made, it escaped through the opening.

I next wished to examine, whether the American poison produced any sensible alteration in the blood of animals, if mixed with it on its issuing warm from the vessels.

For that purpose I cut off a pigeon's head, and received the warm blood in two small conical glasses a little heated, about eighty drops in each glass. In one of them I put four drops of water, and in the other four drops of an aqueous solution of the ticunas, containing scarcely a grain of the dried poison. I shook each of the glasses for a few seconds, so as severally to unite their contents: in two minutes the blood mixed with the simple water was coagulated ; that with the poison did not coagulate, but became of a confiderable darker colour, and in three hours was still in a fluid state, whilft in the other glass the serum and coagulum were distinct.

To have no doubt on this subject, I then tried this poison on parts that are known to poffefs no irritability;

# Vide page 390

and

and I found, says he, that the tendon of a muscle being venomed did not produce the disease of this poison.

I then applied the ticunas to the nerve itself, but in whatever way the experiments were diversified, it does not produce under such trials any derangement in the economy of the living animal.

I next separated the nerve going to the thigh, so that the nervous influence was destroyed: but the venom applied to the muscle of the leg, nevertheless, extended its influence over that limb to the rest of the body. : The AMERICAN POISON then

agrees

with the VENOM of the viper, in being quite innocent to the nerves and tendons, in whatever way it be applied to them ; but, like the viper's venom, it kills in the smallest quantity, if introduced into the blood by the jugular vein, or applied to a muscle ; and its action must therefore be altogether on the IRRITABILITY of the system.

It would be a curious investigation, at the present time, to enquire, " Whether those aerial bodies, which do not 'impart OXYGEN to the blood, produce somewhat similar phænomena with the above poisons, which have been proved to destroy THE IRRITABLE PRINCIPLE;" if so,

we should obtain fome ground for the belief “ that ox" YGEN IS THE PRINCIPLE OF IRRITABILITY.”

In the work of the celebrated Tissot of Geneva, on the nerves, we find him hesitating much in admitting that unrespirable factitious airs kill by destroying the IRRITABILITY of the heart and muscular fibres. “One of the greatest modern naturalists,” says he, “ thinks that their fatal effects are to be explained on this principle; but by what conveyance can their powers reach the heart? How can fixed air kill this way, since, when taken into the ftomach, or applied to the muscular fibres of the intertines, it revives their action, and awakens as it were the very principles of life?”

FONTANA endeavours to overcome this difficulty, by saying that Tissot ought to have had recourse to experiment, to which an authority of so great weight as this benevolent and able physician's is but too capable of preventing an application... The difficulty here opposed is, that we do not know the channel by which mephitic airs deprive the heart of its IRRITABILITY. But it must be acknowledged, continues FONTANA, that the ignorance of one truth does not exclude the knowledge of another; and that we may know the effects, and that it is so, without understanding the cause, and still less their

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