A Mechanical Account of Poisons in Several Essays

by Richard Mead

Besides this Consideration, We must take notice that, the Stomach being distended with Food, presses upon the descending Trunk of the Aorta, and thus causes a greater Fulness of the Vessels in the upper Parts; whereupon the Brain is loaded, or the Derivation of Spirits into the Nerves diminished, and Unactivity or Drowsiness insues. From hence proceed Those Flushings in the Face, Redness, &c. after plentiful Eating or Drinking, most Visible in Those whose Vessels are Lax and Weak, as in Exhausted and Hectick Persons they more especially are.

Thus we may, without the Assistance of the New Chyle entring into the Vessels, account for that Inclination to Sleep which follows upon a full Stomach; Tho’ we must also allow the Distension from This to be a considerable Cause of the same Effect; But this does not happen immediately, nay, sometimes perhaps not within Two or Three Hours after Eating; and therefore the sudden Drowsiness must (as well as the present Refreshment and Reviving which Meat gives) be chiefly owing to some more speedy Alteration.

We come then in the next Place to Opium it self; The Chymical Analysis of which [(147)] does out of One Pound afford of a Volatile Spirit of the like Nature with that drawn from Harts-horn, Five Ounces and Five Drachms; of a fætid Oil, One Ounce Two Drachms and a half; of Caput Mortuum, smelling like Spirit of Harts-horn, Seven Ounces and Six Drachms.

The Virtues therefore of Opium are owing to a volatile Alcaline Salt, intimately mixt and combin’d with an Oily, Sulphureous Substance. The Effects of which We must consider, first of all upon the Stomach, and afterwards, when they have passed the Primæ Viæ, upon the Arterial Fluid it self.

An agreeable Sensation produced in the Stomach, together with a Distension of Its Membranes, we observed before to be the Cause of that Sleepiness to which we are so prone after Eating. The One of These ingages the Mind, the Other acts upon the Body. For Pleasure amuses the Soul, as it were, so that It does not Think, or exercise it self about any outward Objects; that is, Is inclined to Rest. And the Fulness of the Vessels in the Brain Checks and Hinders, in some Measure, the Derivation of the Nervous Juice into the Organs, &c.

Now They who take a moderate Dose of Opium, especially if not long accustomed to It, are so Transported with the pleasing Sense It induces, that They are, as They oftentimes express themselves, in Heaven; and tho’ They do not always Sleep, (which proceeds from the Presentation of pleasing Images to the Mind being so strong, that like Dreams they do over-ingage the Fancy, and so interrupt the State of Rest) yet they do however injoy so perfect an Indolence and Quiet, that no Happiness in the World can surpass the Charms of this agreable Extasie.

Thus We have from this Medicine, but in a far more eminent Degree, all those Effects which we observed to follow upon that grateful Sense in the Stomach, which a moderate Fulness produces. For no Bodies are so fit and able pleasingly to affect our sensile Membranes, as Those which consist of Volatile Parts, whose activity is tempered and allayed by the smoothness of some Lubricating and Oily ones; which by lightly Rarefying the Juices of the Stomach, and causing a pleasant Titillation of Its Nervous Coat, will induce an agreable Plenitude, and entertain the Mind with Ideas of Satisfaction and Delight.

The Case being thus, We easily see upon what Mechanism the other Virtues of Opium do depend, Its Easing Pains, Checking Evacuations, &c. not only in that the Mind being taken up with a pleasing Sense, is diverted from a disagreable One; But all Pain being attended with a Contraction of the Part, That Relaxation of the Fibres which is now caused, eludes and destroys the Force of the Stimulus.

In like manner in immoderate Secretions there is most commonly an Irritation of the Organs, the Removal of which will abate the Discharge. And herein lies the Incrassating Quality of this Medicine, in that the Twitching Sense upon the Membranes of the Lungs, Bowels, &c. being now lessened, the sharp Humor is suffered to lodge there in a greater quantity, before it is so troublesome as to be thrown off and expell’d; it being all one as if there were no Irritation of the Part, if the uneasie Sense thereof be not regarded by the Mind.

These Effects will all be heightened by the Mixture of the Opiate Particles with the Blood; Which is hereupon Rarefied, and Distends its Vessels, especially those of the Brain; and thus does still to a greater Degree lessen the Influx of the Nervous Fluid to the Parts, by pressing upon the little Tubuli, or Canals, thro’ which it is derived.