below, gives way to the sympathy of association[26], the parts coming, by degrees, to perform one uniform action together, which spreads from within to without. When we apply heat to the surface, at this place, we, by continuance, likewise induce the sympathy of association, and the increased action spreads and operates on the disease; but there is this difference, that the action of the heat spreads from without to within, and thus accelerates the progress of the suppurative action. [23] Poultices may also be made, by boiling pounded linseed-cake, or from potatoes, or mashed vegetable leaves (which are the cheapest for hospitals), such as tussilago, &c. [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.