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.