effect; and even from immediate and direct sensations. A person may even feel, that the stomach is the seat of the pleasurable impressions made by opiates. We are to suppose therefore, that vivid vibrations, which, however, lie within the limits of pleasure, ascend perpetually from the stomach and bowels, along the par vagum, and intercostal nerves, up to the brain and spinal marrow, diffuse themselves over these, and from thence descend along the nerves into all the parts of the body. Hence it follows, that they will obscure and overpower all moderate sensations, or vibrations, which subsisted before, or which external objects may from time to time endeavour to excite, and introduce a general pleasurable state over the whole nervous system; with trains of pleasurable ideas, in the manner to be explained hereafter, when we come to treat of ideas, their generation, associations, and dependencies on bodily states. During this pleasurable state, the body will of course be composed to rest; restlessness, tossings, and changes of posture, being caused, for the most part, by uneasy sensations. Hence the blood will be accumulated in the veins and venal sinuses, and grow warm both from the vigorous vibrations excited by the opiate, and from the absolute rest of the body. For absolute rest conduces, in a peculiar manner, to make the body grow warm by the heat reflected from the contiguous coverings; as, on the contrary, the slightest motions frequently returning ventilate and cool the parts. And thus the compression of the medullary substance requisite for sleep will be induced by the action of the opiate upon the stomach and bowels.
But, besides this, we may conceive, that the opiate particles excite vibrations of the same kind in all the parts of the body, after they are taken into the blood, and circulate with it, till such time as, by a perfect assimilation, they lose all their peculiar qualities.
It seems, also, that the continued descent of vibrations, from the brain, and spinal marrow, into the limbs, and external parts, agitates them so much, as to render them unfit for receiving sensation and motion, in the same manner as continued friction of the head, when newly shaved, or shaking the hand, occasion a kind of numbness in the head and hand respectively. For a disorder raised in the motory nerves and muscular fibres, analogous to numbness in the sensory nerves, and sentient papillæ, must produce ineptitude to motion. It seems, therefore, that the insensibility and immobility which proceed from opiates, and which concur in hastening the sleep, and increasing its degree, arise in great part from this cause. The numbness, and paralytic weaknesses, which frequently succeed after opiates, are evidences for what is here alleged.
Opium seems to have an intermediate degree of activity between narcotics, or stupifying poisons, on one hand, and grateful aliments, particularly vinous liquors, on the other. Narcotics operate so violently on the stomach and bowels, the brain, and
