If it seem strange that a Pleasure in the Stomach should so powerfully Influence the Mind; let it be considered, on the other Hand, how violent Effects, an uneasie and disagreeable Sense in the same Part does produce; what a terrible Agony Two or Three Grains of _Crocus Metallorum_ throws the whole Fabrick into; how readily the Fluid of the Nerves is with a more than Ordinary _Impetus_ determin’d and commanded into the Muscles of the Stomach and _Abdomen_, in order to throw off the Enemy, and remove the ungrateful Sensation. Now the Consequences which we have ascribed to a pleasing Sense in this Part, are only just the contrary of these we find the opposite Affection of Pain induces. And indeed _Pleasure_ and _Pain_ are Two great Springs of Action in the Animal Œconomy; The Changes they make in the Fabrick are the Causes of many Effects which seem surprising, because we do not regard the Mechanism by which they are produced: but these must be more considerable in the Stomach than any where else; This Part being, for very wise Purposes, of so acute a _Feeling_, that some Philosophers have for this Reason thought It to be the Seat of the Soul. 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.