This action, as well as every other, is much modified by the importance of the part which is the source of the action, and by the constitution of the patient. It is more severe in children than in adults. The affection will be more fully detailed, when treating of local injuries, and the management of patients after severe operations. The _Causes_ of Inflammation come next to be considered; and first, of the proximate cause or theory. The different states of the Vessels, in their healthy and in their incited condition, have given rise to much discussion. In the first place, considerable difference of opinion exists as to the relative share which the heart, the larger arteries, and the capillaries, have in propelling the circulating fluid in a state of health. Some physiologists are inclined to attribute the principal power to the heart, the blood being propelled and returned, according to them, almost entirely by the vis a tergo; while they suppose that the arteries possess merely a degree of elasticity or tonicity. Considering the arteries as elastic tubes, performing an indispensable part in the propulsion of the blood, we will now briefly consider their state in inflammation. Passing over the different theories of error loci, spasm, &c., which have at various times been entertained, let us first examine the condition of the capillary vessels, for these are primarily and principally concerned. In inflammation, the balance of the circulation is destroyed, but a diversity of opinion has existed as to the precise nature of the change which occurs. It has been supposed, and perhaps correctly, that the circulation is, in the first instance, much accelerated in the capillary vessels of an inflamed part; but it has been satisfactorily proved by experiment, that, after inflammation is fairly established, the blood circulates more slowly than in the healthy state of the vessels. There appears, in fact, to be, as insisted upon by some writers on the subject, a state of excitement, then of collapse, followed, if the life of the part is not destroyed, by reaction. When a part is stimulated, the circulation is accelerated, and a greater quantity of blood is transmitted by its vessels: if the excitement is speedily removed, they recover themselves, though perhaps a little dilated, and no inflammation ensues. If, for instance, a foreign body of any kind gets entangled betwixt the upper eyelid and the bulb of the eye, and it is permitted to remain a few moments only, redness of the whole surface of the conjunctiva takes place, but it is transitory, and disappears entirely some short time after the extraction of the foreign body. If, however, it is permitted to continue longer in contact with this sensible surface, the membrane reddens more and more, and becomes thickened. Violent pain, with discharge of tears, and alteration of the secretion from the mucous surface, take place, ophthalmia is, in fact, established. If the