embrocation is made, may contribute according to its particular qualities. Hence embrocations are also of use in resolving obstructions.
In all these cases the violent vibrations, which ascend along the nerves of the injured part, must be communicated in a particular manner to the neighbouring branches, and occasion a slight inflammation, i.e. a soreness, there. This soreness is not perceived while the original inflammation subsists, being obscured by it. The vibrations in the neighbouring nerves may also be increased by the cessation of violent ones in the place of original inflammation. Hence the soreness of the neighbouring parts after colics, head-aches, &c. The pain in the external parts of the head, which follows a debauch, i.e. an inflammation of the brain, and its membranes, may be of the same kind.
These hints may serve to shew, that the doctrine of vibrations is as agreeable to the phænomena of wounds, burns, &c. as any other yet proposed, or even more so. But much farther inquiry is requisite.
Itching often attends the beginning and ending of inflammations, and particularly the eruption of inflammatory pustules. We may conclude therefore, according to the foregoing account of inflammations, that itching is caused by a moderate increase of vibrations, in a part of small extent.
It is agreeable to this, that the lodgment of the perspirable matter, or other cutaneous secretion, when hardened, occasions itching; for it is easy to conceive, that in these cases, an obstruction and slight inflammation in the small vessels of the skin may arise.
Pressure, which allays itching, may be supposed to do this by checking the vibrations.
Scratching may convert it into a pleasure, by communicating the increased vibrations to the neighbouring parts, in such a degree as falls within the limits of pleasure. And as this freer communication caused by scratching may increase the vibrations in the neighbouring parts, so it may lessen those which subsisted before in the point that itched, thus reducing all to an equality, or nearly so. At the same time it appears, that rude or long-continued scratching must, by the increase of vibrations, which it occasions, also by laceration, increase the heat, inflammation, and itching, and even end in pain.
Friction of the skin, without previous itching, excites a pleasurable sensation; and also ends in inflammation and pain, when carried too far, for the like reasons.
Since extreme parts are more apt to receive an increase of vibrations than others, as has been observed; it appears, that the
