[24] The inflammatory action, when moderately strong, acts naturally as an exciting cause, inducing the purulent action, which is therefore said to be a termination of inflammation. It is therefore as unnecessary to interfere in the production of this secretion, when the action is of proper strength, &c. as it would be to attempt to increase, by local means, the vesication which is produced by a blister. Poultices are, in this condition, perhaps chiefly useful, by removing the causes which tend to abate the action at an improper time, such as those which produce resolution, as cold, &c.
[25] They keep up the heat of the part, and keep it moist until this happens, and prevent the action from flagging suddenly, which is all that is required of them, when the action is going on of itself in a proper degree.
[26] When two parts are affected at the same time, in consequence of an agent operating quickly on one of them, they commonly exhibit the sympathy of association, which takes place suddenly, but generally at first lasts only for a short time, if the parts be distant; but, if the original disease still continue, it may spread, inch by inch, until it arrives at the part which was formerly affected, and which is again affected more permanently, by the same kind of sympathy taking place, but in a different way. In the first case, we have the sympathia consociationis interrupta; in the second, the sympathia consociationis serpens. It is this last which is the cause of the extension of all action in a part, and which, when strongly excited, overcomes the natural tendency to the exhibition of the sympathy of equilibrium. It is, however, more difficult for local action to spread by degrees to parts which evince the sympathy of equilibrium than other parts; and these, in general, are longer of being affected. Thus, when inflammation begins in the skin, it can much more easily spread along the skin than dip down to the muscles.
[27] In proportion as the action extends outward, it also becomes more concentrated. An abscess is therefore somewhat conical, or at least hemispherical, the base being turned inward, and the apex outward. When the action reaches the surface, it is first at a single point; but, by degrees, it becomes extended, and the apex becomes broader.
[28] Such as the thorax, trachea, &c. Instances have happened of suffocation being thus produced.
[29] Although, in general, an abscess has little tendency to extend itself deep down, but rather moves toward the surface, although so far from it originally, that, had the action extended equally in all other directions, the size of the abscess must have been immense; yet, when it is situated over a cavity, it may proceed toward that as if to an external surface. Even, however, in this case, the general law, of all actions tending to the skin, obtains; for the progress outward is much quicker than that inward; but, if the action commenced near the surface of the cavity, as is commonly the case, the difference of the distance will compensate for the superior tendency to extend outward; and, therefore, the abscess may burst at the internal surface into the cavity.
[30] In abscesses seated on the thorax, I have known the intercostal muscles and pleura continue the suppurative action, after the external surface had opened, and thus an opening came to be formed into the thorax.
[31] This likewise affects the system, and produces syncope, if the mechanical support be withdrawn suddenly from the parts.
[32] This poultice does not require to be so hot, nor changed so frequently, as before the full formation of matter.
[33] If this produces pain, we may in general conclude that it has been used too soon.