[(145)] Pag. 176. seq.
[(146)] Hist. Plant. l. 9. c. 16.
ESSAY IV.
OF OPIUM.
The Ancients having Experienced that Opium would oftentimes Kill, though taken in no large quantity, ranked It with Poisons, and gave It the first place among Those, which from their Stupefying Quality They call’d Narcotic.
True indeed it is, that We do every Day find This to be, in a small Dose, one of the most Noble Remedies in the World. But it is not worth the while to engage in the Controversie warmly debated by some Authors, how far Poisons are Medicinal; since it is notorious enough, that Medicines do sometimes prove Poisonous. And take the Matter as We please, it may serve to very good Purposes to understand the manner of Operation of so Celebrated a Drug, and help Us in a great Measure to ascertain Its Use in different Cases, if we are beforehand rightly apprised of Its Nature and Way of Acting.
In order hereunto, it is necessary, besides some other Præcognita, since one of the chief Virtues of this Medicine Is Hypnotic, to Define distinctly what Sleep is, or rather, (to avoid Confusion and Disputes about Words) what Difference there is between an Animal Body when asleep and when awake. For I suppose the History, Manner of Preparing, &c. of Opium, to be already sufficiently known.
First then, There is no One but knows that in Sleep there is a Cessation from Action. When Waking, We Walk, Discourse, Move this or that Limb, &c. but in natural and undisturbed Rest there is nothing of all These; that is, whereas being awake, We do perform several Motions by the voluntary Contraction of our Muscles; when asleep, those Muscles only are Contracted, whose Action is in a manner Involuntary, or to which the Mind has always so constantly determin’d the Spirits, that It does it by a Habit, without the Intervention of the Reasoning Faculty; such are Those of the Heart and Breast.
So that there is at this time a kind of Relaxation or Loosness of the moving Fibres of the several Members; or at least such a quiet Position and State of them, by which all the Antagonist Muscles are in an Æquilbrium and Equality of Action, not overpowering one another. For this indeed seems to be one great Design of Sleep, to recover to the Parts overstretched by Labour their former Tone and Force; and therefore we do naturally, when composing our selves to Rest, put our Body into that Posture which does most Favour the particularly wearied Limbs, and conduce to this end.
In the next place, it is very plain that there is in Sleep not only a Rest and Suspension from Acting of most of our Bodily Organs, but even of our Thinking Faculty too. That is (for I would prevent Cavils) a ceasing from such Thoughts as when Waking We are exercised about, which we do Reflect upon, and Will to employ our Mind with. For though Dreams are Thoughts, yet they are but imperfect and incoherent Ones, and are indeed either so faint and languid Representations, as to be consistent with our Sleep, as some may be; or else if they be strong and lively, they are, as every one knows, the Interruption and Disturbance of It.