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manner of acting. The question is reduced to this, to
determine by experiment,
"Whether thefe mephitic va-

66

pours deftroy, or do not deftroy, the irritability of the "heart;" and the difficulty propofed above is of no weight, whether we know or not the way in which this is brought about, provided the experiment be certain, and the illuftrious writer oppofe nothing which disproves it.

In confequence of these confiderations, I formed to myfelf, fays FONTANA, a refolution to try different mephitic gases, and to examine their effects on living animals. I was affifted by CAVALLO, in company with other philofophers. The refult of all our experiments demonftrated, that mephitic vapours kill animals, by deftroying the IRRITABILITY of the whole muscular fyftem.

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In one experiment I placed a frog in unrefpirable air (fuch as does not impart OXYGEN to the blood). It died almost instantly, after making a few leaps, and being violently agitated. I opened, and found all its parts flaccid and relaxed. The beart ftill moved, but feebly, and with great difficulty, and in a fhort time entirely loft these flight remains of action. I endeavoured ineffectu ally to irritate, not only that, but likewise the ather mufcles; neither of them would contract. I forced a needle

needle into the fpinal marrow, and faw, with furprise, that it no longer awakened the motion of the limbs. The colour of the red blood was also wholly changed to a brown.

I placed two frogs beneath a glass recipient, into which I had introduced the gas obtained from a folution of ironfilings in the nitrous acid. They also died inftantly. I opened them, and found the arterial blood of a brownish bue, and collected in the aurieles. The heart was no longer in motion, and was infenfible to ftimulations. The flesh was thoroughly flaccid, and had lost all irritability. On pricking the crural nerves, the leg remained motionless.

The illuftrious GIRTANNER injected into the jugular vein of a dog a small quantity of azotic air. The animal died in twenty feconds. Upon opening the thorax, the pericardium, and the heart, the right auricle and ventricle were filled with black blood. The left ventricle was of its ordinary dark colour. The heart, and all the muscles, had loft their irritability almost entirely, and contracted but weakly upon the application of the strongest ftimuli, such as the electric spark.

A fmall quantity of carbonic acid gas was injected into the jugular vein of a dog. The animal became fleepy, 3 F 2

and

and died in about a quarter of an hour. The right auricle and ventricle of the heart were filled with dark blood. The blood contained in the left ventricle and auricle was of a deeper colour than ordinary. The heart and muscles had lost all their irritability.

This important fubject demands more comparative experiments, and made exprefsly for this purpose; and we could with that a diftinguifhed phyfician, who first brought this fubject into repute in ENGLAND, would examine into it minutely, and extend this principal branch of modern medicine. We do not here demand fresh, fublime, and abstracted theories, which a fingular effort of genius gave birth to: we are in need of nice obfervations; new and well-imagined experiments; direct and ufeful inductions, drawn by a calm mind, and one capable, like his, of affembling and combining in the beft manner the most luminous particulars.

I cannot forbear mentioning in this place the fingularity of a small microscopical animal, which LEWENHOECK has named Rotifer, wheel-polypus. It is a small gelatinous worm, commonly found in the earth or fand collected by rain in the tops of houses. I have likewise found it in other earths, as well as in waters that have been some time stagnant, and more frequently again in

thofe

thofe that have a gentle current, and are filled with conferva, and other aquatic plants. This worm is divided towards its head into two tolerable fized trunks, which appear like two stars, from the number of fmall, extremely sharp, and short branches, which project from it. They really appeared to LEWENHOECK to be wheels of a rare mechanism, and every one would judge the fame on seeing the creature put them in motion. But a more exact obfervation at length convinced me, that they are not wheels, but a quantity of moveable arms regularly planted all around the two trunks. It moves these one after another with so great celerity that the eye fancies it fees abfolute wheels: but to be certain of the contrary, it is only neceffary to place it betwixt two pieces of glass, and then observe it a long while together with an excellent microscope. In fwimming it strikes the water with these arms or branches with incredible celerity, refts itself at different periods, and thus tranfports itself from one place to another. When it eats, it, on the contrary, fixes its tail in fome fubftance, and afterwards turns its two wheels, giving fuch a motion to the water, that it directs the course of it towards its. head, so that it prefents to its mouth all the small corpuscles with which stagnant water abounds.

The

The wheel-polypus, I have spoken of above, lofes when dried every kind of motion and appearance of life, and recovers both the one and the other when again put into water. I placed one of them on a bit of glass, which I expofed, during a whole fummer, to the noon-day fun: it there became fo dry, that it was like a piece of hardened glue. A few drops of water did not, however, fail to restore its motion and life. Laftly, I left it, by way of experiment, in a very dry foil, and expofed, during the fummer, to the whole heat of the fun for the space of two years and a half. I afterwards returned it again into water, where, at the end of two hours, it recovered life and motion. The water appears in this cafe to be decompofed when it comes in contact with the animated fibre, the OXYGEN it contains combines with the fibres of the rotifer, restores its irritability, its life, and organic motion, of which it had been deprived by the exceffive ftimulus of heat, to which it had been fo long expofed.

The microfcopical eels that are found dry and withered in smutty wheat, recover motion and life as foon as they are wetted with a little water, and again become lifeless and dry, whenever they are no longer expofed to water. I have repeatedly affured myself of this with an Thus then do they preferve the power

extreme pleasure.

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