By this contrivance, we obtain a firm covering to the granulations, and bring a substance in contact with each individual. We then restore, as it were, the natural state of the parts, each granulation having a substance in contact with it; and a slight interstice is left between each, owing to their pointed structure. They become, therefore, similar, in this respect, to the organic particles of internal parts; on which account, healing goes on more quickly, and the organic particles, or granulations, are deposited in greater perfection, and with greater powers of action; for the unusual and morbid condition of exposure and want of contact is now removed. The same circumstances promote cicatrization, when the granulations have risen to a proper height. This is more evidently seen in the cure which is effected of the smaller ulcers, by dusting them with chalk, &c. or dressing them with an ointment made thick with some mild powder, by which a scab, or covering, is formed, which operates clearly independently of pressure. Pressure, applied with this view, ought to be moderate and permanent, and may be used with utility in almost every case of solution of continuity, however healthy the action may be. But, besides being of use in this way, pressure also produces a second set of effects, by mechanically exciting action in the part to which it is applied. Applied to the skin, it increases the cuticular action, and the skin is formed thicker. Applied to a weakened part, it increases the natural action of that part, and strengthens it: This is seen in the instance of debilitated muscles, &c. But, if the pressure be too great, then a morbid increase of action takes place, which even goes the length of inflammation, if the pressure be considerable; and this inflammation is either strong or weak, according as the pressure has operated; for, if many vessels be obstructed, as is commonly the case, then the power of the part is injured, and the action is weak; or, the same happens if pressure be applied in any manner to a weak part, or if the constitution be weak; as, for instance, from previous disease.
Pressure, applied to a part, increases in particular the functions of absorption and deposition. If moderate, these functions are moderately increased, and the structure of the part continues either the same, or it augments in size, as we observe, in the effects of walking, on the skin of the feet; but, if the pressure be greater, then these functions are morbidly increased, the particles are deposited imperfectly formed, and are as quickly taken up. The structure is therefore destroyed, and a vacuity formed. These effects are produced more easily upon diseased than healthy structures; because their powers of acting, and sustaining action, are less. Friction is in this respect similar to pressure.