A Mechanical Account of Poisons in Several Essays

by Richard Mead

’Tis a small Grotta at the Foot of a little Hill, about Eight Foot high, Twelve long, and Six broad; from the Ground arises a thin, subtle, warm Fume, visible enough to a discerning Eye, which does not spring up in little parcels here and there, but is one continued Steam, covering the whole Surface of the bottom of the Cave; and has this remarkable difference from common Vapours, that it does not, like Smoak, disperse it self into the Air, but quickly after its rise falls back again, and returns to the Earth; the Colour of the sides of the Grotta being the measure of its Ascent; for so far it is of a darkish Green, but higher, only common Earth, and this is about Ten Inches. And therefore as my self found no Inconvenience by standing in it, so no Animal if its Head be kept above this Mark is in the least injured: But when (as the manner is) a Dog, or any other Creature, is forcibly held below it, or by reason of its smalness can’t hold its Head above it, It presently, like one stunn’d, loses all Motion, falls down as Dead, or in a Swoon, the Limbs convuls’d and trembling, till at last no more sign of Life appears than a very weak and almost Insensible beating of the Heart and Arteries, which if the Animal be left there a little longer, quickly ceases too, and then the Case is Irrecoverable; But if snatch’d out, and laid in the open Air, soon comes to Life again, and sooner if thrown into the adjacent Lake.

In this short, but accurate, History of the Grotta de Cani, I have set dow those Particulars which do not only distinguish Mephitical Exhalations from common and innocent Fumes, but also give hints sufficient, I think, Mechanically to determine the Reason and Manner of their surprising Effects.

And not to spend time in refuting the Opinions of Others, I shall only take Notice, that here can be no suspicion of any true Venom or real Poison; if there was, it were impossible that Animals taken out of the Grotta, should so immediately recover the Effects of it, without any remaining appearance of Faintness and Sickness, or such like Symptoms as those suffer who have been breathing in an Air impregnated with malignant corrosive Effluvia. Besides, that the Venomous Corpuscles would certainly, in some Degree at least, infect the Air in the upper Part of the Cave, which continues pure, and fit for Respiration. Neither indeed after what manner soever this Poison be imagin’d to Act, whether by dissolving or coagulating the Blood, could its Efficacy be so sudden and momentaneous, without some Marks of it in the Creatures kill’d, when opened, which yet do discover nothing of this Nature extraordinary, neither in the Fluid, nor in the Solid Parts.

In order therefore to understand wherein this deadly quality Consists; I say in the first Place, that Life, so far as it respects the Body, is, in one Word, the Circulation of the Blood; that is, its Motion in Conical Distractile Vessels from the Heart to the Extreme Parts, and its Return to the Heart again by the same Canals inverted; For ’tis upon this that all Animal Functions, all Sense and Motion Voluntary and Involuntary, do depend; so that the Regularity of this Course is the Measure of Health, or the most perfect Life, as its various Irregularities are the Occasions of Sickness and Diseases, or a beginning Death.

Now all the Animal Operations and Offices which proceed from this Circulation, are the Effects of several Secretions of Liquors of very different Natures out of the same Fluid Mass; It was therefore absolutely necessary that the Blood, before It be distributed to the Organs, should be so comminuted and broken, as that no Cohæsion of its Parts should hinder the Separation of these Juices from It, when it Arrives with a determinate Force at the Orifices of the Secretory Vessels.

This Work is done in Its Passage thro’ the Lungs, by the repeated Compression of the Air in those Bladders upon the Arteries, with wonderful Contrivance dispers’d among ’em [(160)]. Herein lies the Use and Necessity of Respiration; and the sudden Mischief of Stopping it, in that the whole Mass of Blood being to pass this way, upon a Check here, there presently insues a Stagnation, that is, a Cessation of all Animal Functions, or Death; Which will be the more speedy, if not only no Air is inspired, but a Fluid of a quite different Nature from It succeeds in its Place.

Wherefore it must be observed, that this good Effect of the Air is performed by its Elasticity; And that no Fluid whatsoever, that we know besides, is Elastic, at least to any considerable Degree, that is, has a faculty of expanding and dilating it self when compressed; No, not Water, as near as That is thought to approach to Air in its Nature.

And now as to the present Case, I took notice before that this Vapour is one continued and uninterrupted Steam, and that quickly after Its rise it falls down again; that is, that it has little or no mixture of Air with It, or no Elasticity; and is, on the other Hand, very heavy, when forsaken by the Force of Heat that drove it upwards.

So that I make no Question, but that Animals in this Place do instead of Air inspire Mineral Fumes, that is, a thin watery Vapour, impregnated with such Particles as do, when united together, compose solid and heavy Masses; which is so far from helping the Course of the Blood thro’ the Lungs, that it rather expels the Air out of the Vesiculæ, and straitens the Passage of the Blood Vessels, by its too great Gravity; whereupon the Bladders are relaxed and subside, and the Circulation is immediately Interrupted. But if the Animal be in time removed out of this Steam, that small Portion of Air which does after every Exspiration remain in the Vesiculæ, may be powerful enough to drive out this Noxious Fluid; especially if the Head of the Creature be held downwards, that so its Gravity may forward its Expulsion; or It be thrown into Water, which by assisting, upon the account of its Coldness, the Contraction of the Fibres, promotes the retarded Circle of the Blood; as we every Day experience in a Deliquium Animi, or Swooning Fit.

Tho’ if this Stagnation be continued too long, no Art can renew Life, no more than in One perfectly strangled; nor will the Lake of Agnano it self be of any Service; which shews that there is no singular Virtue in That Water beyond any other; nor is it, as some have fondly Imagin’d, a Peculiar Antidote to the Poison of the Grotta.