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of my pushing the fucker, owing to its not being exactly fitted to the fides of the fyringe: I obferved to the perfons prefent, that the experiment had failed, but was furprised to hear in 'reply, that the animal was dead. I do not think ten feconds paffed betwixt the time of the liquor's flowing back, and the death of the animal, which had actually taken place. I cannot eftimate the quantity of poifon introduced into the blood, but as the animal died, fome must neceffarily have found its way thither; had not this happened, I fhould have fuppofed, from the quantity which flowed back into the tube, that not a fingle drop of it had entered the jugular vein.

Having put my fyringe in better order, I introduced, fays he, two drops of water, with which I had previously mixed about a quarter of a drop of the aqueous folution 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 ftruck by lightning. I do not think half a drop was introduced.

The death of these animals was more fudden than in the cafes of introducing in a fimilar 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

bit by the viper, the blood is often coagulated in the veffels, and partly fluid; in those destroyed by the ticunas it is always fluid. As the coagulability of the blood is governed by the fame 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 poifon of the ticunas is fatal to almost every species of animal †. The muscles of the animals who are killed by the ticunas appear remarkably pale. The blood in the venous vessels near the heart is darker than usual, and not coagulated. The abdominal vifcera 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 For lefs fpotted; the fpots were frequently very large and

livid.

This change in fo noble an organ deferves the utmost attention. It was nearly the fame 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 fo tenacious are they of life, that each part will remain for a long while irritable. This principle is fo predominant in their nature, that few poifons are able to overcome it. Some adders, upon the application of the ticunas, feemed indeed, however, lefs lively than ufual, and the hinder part of the body, which was wounded, became benumbed, and loft its natural motion in a fenfible degree, and that for several hours; but none died from this poifon.FONTANA.

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venom of the viper *. very visible through the external membrane, when examined with a microscope; and upon a puncture being made, it escaped through the opening.

The air within the cells was

I next wished to examine, whether the American poifon produced any fenfible alteration in the blood of animals, if mixed with it on its iffuing warm from the veffels.

For that purpose I cut off a pigeon's head, and received the warm blood in two small conical glaffes 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 poifon. I fhook each of the glaffes for a few seconds, fo as severally to unite their contents: in two minutes the blood mixed with the fimple water was coagulated; that with the poifon did not coagulate, but became of a confiderable darker colour, and in three hours was still in a fluid ftate, whilft in the other glass the ferum 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.

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and I found, fays he, that the. tendon of a mufcle being venomed did not produce the difeafe of this poison.

I then applied the ticunas to the nerve itself, but in whatever way the experiments were diverfified, it does not produce under fuch trials any derangement in the œconomy 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.

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It would be a curious investigation, at the present time, to enquire," Whether thofe aerial bodies, which do not impart OXYGEN to the blood, produce fomewhat fimilar phanomena with the above poifons, which have been proved to destroy THE IRRITABLE PRINCIPLE;" if so,

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we fhould 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 hefitating much in admitting that unrefpirable factitious airs kill by destroying the IRRITABILITY of the heart and mufcular fibres. "One of the greatest modern naturalists," fays 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, fince, when taken into the stomach, or applied to the muscular fibres of the intestines, it revives their action, and awakens as it were the very principles of life ???

FONTANA endeavours to overcome this difficulty, by faying that TISSOT ought to have had recourfe to experiment, to which an authority of fo great weight as this benevolent and able phyfician'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 caufe, and still less their 3 F

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