Mortification, to a greater or less extent, may be produced in any constitution, and at any age, by the application of heated substances, caustics, acids, &c.; by the effusion of acrid matter into the cellular substances, as urine or putrid sanies; by the interruption of the circulation and nervous energy, as from ligatures or improperly applied bandages—or by natural strictures, as those in hernia and paraphymosis; by continued pressure, more especially in such patients as have, from long suffering and confinement, had the powers of the circulating system weakened; and by violent contusions, as in fractures, compound luxations, and gunshot injuries. A frequent source of mortification, in inclement seasons and climates, is exposure to extreme cold. In this case, the cold is not the direct, but the indirect cause; the power of the parts is very much weakened by exposure to the low temperature, and is thereby rendered incapable of resisting the incited action which follows the stimulus of sudden transition from cold to heat, even though the degree of increase in temperature should not exceed that of the natural standard. That cold is not the direct cause of mortification, has been undeniably proved by facts derived from military practice. No symptoms of inflammation or gangrene occur when the soldier is on duty, and continuously exposed to severe cold; but they speedily present themselves after a rapid thaw has commenced, or after the soldier has imprudently approached a fire. Soon after the half-frozen person has begun to feel a little more comfortable from sudden warmth, he becomes aware of pain, attended with a sensation of itching in the extremities, generally the lower, which are considerably swollen, and of a dull red colour; these, and other symptoms of inflammation, are of no long duration, the action speedily runs its course, and the part soon plainly indicates that gangrene has commenced. When gangrene follows the tight application of a ligature, the death of the part seems to depend more on obstruction to the circulation of the blood, than on any diminution of the nervous energy, for we do not observe that paralytic limbs are peculiarly liable to gangrene. The surgeon frequently takes advantage of the fact that a part soon dies when its supply of blood is cut off, or its return in the veins interrupted; and has recourse to ligature for removal of parts, When he considers it inexpedient to employ cutting instruments. Mortification may be produced by the above-mentioned causes, either immediately or consecutively; and it will occur in some constitutions, or states of constitution, at some periods of life, in some structures, and in some parts of the body, more readily than in others.