solid parts with fluids, from the solvent action of the gastric juice, or from incipient putrefaction.

Fatty Degeneration.-Another organic result of depression is fatty degeneration. It has long been known that flesh, under certain circumstances of exclusion from atmospheric air, is converted into a fatty matter called adipocire. This fact suggested to Dr. C. J. B. Williams that the fatty degeneration occurring during life might be equally a result of chemical action. Dr. Quain found that, by immersing muscle in dilute acid, so as to prevent the putrefactive process, the pathological fatty degeneration of that tissue might be closely imitated. The inference from these facts is, that, when the organic tissues are so far withdrawn from vital influences as to allow the predominance of chemical affinities, without being completely surrendered to them as in putrefaction, the tendency of these tissues is to yield fatty matter as one of the results of their decomposition. If, therefore, any part is greatly depressed, whether from the want of due vital influence, or from an insufficient supply of material for its nourishment, chemical reactions may take place, by which the tissues of the part may to a greater or less extent be converted into fat, the other products of the decomposition being carried off by the absorbents, or in some other way eliminated. There is reason to believe that this result very frequently takes place. It is of no consequence whether the depression is indirect, as in the advanced stages of inflammation, or direct, as when a due supply of blood is withheld. The formation of pus, one of the first results of depression in inflammation, is always attended with the production of fat, and the degeneration of the pus corpuscle into the granule-cell has been shown to be mainly an oleaginous transformation. It is probable that the pus corpuscle differs from the fully formed exudation corpuscle in which it originates, simply in the loss of vitality in the latter, and the consequent generation of oil within it. In fatty degeneration of the heart, liver, and kidney, from depression of the nutritive function, oil may be seen, upon microscopic examination, occupying the place of the proper muscular structure within the sheaths of the fibrils, and of the proper contents of the secreting cells in the glandular parenchyma. This sort of fatty degeneration is wholly different from the excessive secretion of fat which results from an overabundance of the material of nutrition, or an overaction of the nutritive function, constituting morbid obesity. In the latter case, fatty matter is deposited in addition to the normal structure, and, if it interfere with it, does so by producing absorption through pressure. In the former case, the normal structure itself undergoes degradation.

Calcareous Degeneration. This is still another organic result of depression. In this affection molecules of earthy matter, generally with a calcareous base, take the place of the normal tissue, and often to such an extent as to give an almost bony hardness to the part. It is very apt to occur in the coats of the blood-vessels; but may take place in any of the tissues, and, indeed, is frequently found in abnormal structures or deposits, as in the false membrane of inflammation, in tubercle, and in cancer. Whether it is the result of the disintegration of the tissue leaving its earthy components behind, or a direct deposition from the blood, supplying the place of the absorbed structure, has not been determined; but the probability is that it proceeds from both these sources. It is very analogous to the fatty degeneration, occurring under the same circumstances, and not unfrequently along with it. Both are very common in the old, in whom they seem to be regular consequences of the failing powers and actions of life, rather than morbid changes; capable it is true, like other normal processes, of producing injury by excess or malposition, but on the whole forming one of the physiological series of vital processes beginning with the impregnated germ, and ending with the last breath of expiring old

age. The arcus senilis, or grayish-white circle often observable in elderly persons near the edge of the cornea, has been ascertained to be a fatty degeneration, generally coincident with a similar change in various internal parts of the body; and the ossification of the arteries, so common in the same class, is an example of the calcareous degeneration.

Gangrene. This has already been defined to be 'the death of a part, without the death of the whole body. From whatever cause it may remotely proceed, it is obviously the direct and the last result of a state of depression. If it follow an excitement too violent for the vitality of the part to support, it is nevertheless the immediate consequence of the depression which necessarily ensues after such excitement. If it result from inflammation, through the interruption which this sometimes produces in the supply of blood, the direct cause is still the depression which arises from the absence of the vital and essential stimulus. If it be traceable to a complication of certain morbid poisons or depraved states of health with inflammation, such as occur in anthrax, hospital gangrene, malignant pustule, &c., it is to the depression occasioned partly by the direct agency of the superadded cause, partly by the exhaustion consequent upon the inflammatory excitement, that the gangrene is to be ascribed. But it is often also the direct result of depression, without any preexisting inflammation, or excessive action in the part affected. Such is the case with gangrene following an interrupted supply of blood, occasioned by pressure upon the arteries, by the accidental destruction of the vessels, by the obliteration of their cavities by means of coagulated blood or fibrin, or by certain diseases of the heart, which disable it from transmitting to the extremities the necessary quantity of blood for the support of their vital actions. Such also is the case with the gangrene produced by certain positively depressing agents, as excessive cold, large quantities of ergot, and local violence so great as to destroy the life of the part without reaction.

There is in gangrene a total absence of all the phenomena of life in the part. There is no sensibility, no circulation, no active movement whatever, no generation of animal heat. But these are not unequivocal signs of the loss of vitality. They may all exist, and yet the part may be living, and, with proper care, may be restored to its healthy actions, as not unfrequently happens after the apparent death of a part from cold, violence, or some mechanical interruption to the circulation. It is of the greatest practical importance that, in such cases, the apparent should not be mistaken for real death, to the neglect of proper measures of restoration. The only certain sign that mortification has really occurred is the commencement of putrefaction. This, under ordinary circumstances, always takes place sooner or later after the death of the part. But, though it is indispensable as a sign, gangrene may occur and continue to exist for a considerable time without it, as when resulting from cold, or in parts destitute of fluids or secluded from the air. Sometimes putrefaction is concurrent with the mortification, especially when the latter is the consequence of inflammation, and the part is exposed to the conjoined influence of air, moisture, and warmth. Besides loss of sensation, vital movement, and animal heat, there is generally, even in cases where putrefaction has not taken place, a change of colour and consistence, dependent partly upon alterations antecedent to the loss of vitality, partly upon those simultaneous with the mortification. Putrefaction is the decomposition which occurs under the influence of chemical affinities. In this condition, there is an offensive odour consequent upon the disengagement of fetid gases, usually more or less emphysematous swelling, infiltration with dark, turbid liquid, and a loss of cohesion. In some instances, however, as in dry gangrene, the parts are hard, shrunk, and dry, like the flesh of mummies; and the smell, though fetid, is much less so than in ordinary cases.

In the state which precedes gangrene, in that which is presented by the living parts in the vicinity of the dead, in the progress of the affection, and in the earlier or later occurrence of putrefaction, there are sources of such diversified and complicated phenomena that it would be wholly out of place, in a general treatise, to attempt to describe all their possible combinations. When the gangrene has originated in inflammation, the phenomena of the latter affection in its various stages, are mingled with those of the former. It may be proper to mention here that, though sensibility is usually diminished in the progress of the mortification, violent pain is sometimes experienced, as in the gangrene which attacks the extremities of old persons. In such cases, it is possible that the nerves may preserve, for a time, their vitality in the midst of the mortified structure, and thus be exposed to irritation from the contact of what has now become foreign matter. Sometimes the mortification advances gradually without any apparent disposition to set limits to its extension, till it has destroyed the life of the patient. Generally, however, it is either confined to the spot originally affected, or is arrested at some point of its progress; in which case, inflammation occurs in the living parts in contact with the dead, and the latter are separated by ulcerative absorption, as already described under the head of inflammation. Occasionally, when the constitutional tendency to gangrene is strong, mortification recommences, after having been temporarily arrested; and this alternation may occur several times, till at length the affection ceases, or the patient dies. The period required for the separation of the slough is exceedingly various, according to the vigour of the constitution, and the nature of the part affected. Under favourable circumstances, as in persons of good constitution and previously vigorous health, and in soft highly vital parts, the separation is effected in eight or ten days; but, under opposite circumstances, it is sometimes greatly protracted, even to two or three months or more.

The degree of danger from gangrene varies with its extent, the importance of the organ affected, the previous condition of the patient, and the nature of the attendant diseases. When external, and of moderate extent, it seldom proves fatal; while a patient often very rapidly succumbs under a very limited internal mortification. Still, life is sometimes preserved, though a considerable portion of some internal organ may be gangrenous. Large portions of the bowels have sloughed away, and been discharged per anum, and yet the patient has recovered. A previously feeble state of health, or the coexistence of some depressing malady, very greatly increases the danger. In cases of internal gangrene, the danger is also increased by the liability to the absorption of the offensive and depressing products which result from putrefaction. Other sources of danger, in cases of extensive gangrene, are hemorrhage from the sloughing of large arteries, and the exhaustion consequent upon excessive suppuration, during or after the separation of the slough. Gangrene has some. times proved curative by attacking exclusively some morbid structure, as the cancerous, for example, which, if not thus destroyed, would have gone onward to a fatal issue. As gangrene presents phenomena somewhat different according to the tissue which it occupies, it will be proper to trace it, at least briefly, through the different tissues.

In the areolar or cellular tissue, gangrene is very apt to occur as a consequence of carbuncle and erysipelas phlegmonodes, and when parts in a state of ordinary inflammation are bound down by strong fibrous expansions. It is sometimes in this situation very extensive, destroying the cellular tissue which connects other structures, and dissecting out, as it were, muscles, tendons, blood-vessels, and nerves. When it affects the subcutaneous cellular or adipose membrane, the skin over the part affected often assumes a gangrenous

appearance, and portions of it slough away, or numerous orifices are made by ulceration, so as to permit the escape of the dead tissue. The colour of cellular membrane, in a state of gangrene, is a dirty-white, or yellowish-white. By putrefaction it is converted partly into a grayish, very fetid pulp, which is often mixed with pus, and more or less with blood. When discharged through ulcerated openings in the skin, it often has the appearance of wet tow.

The serous tissue seldom mortifies, unless in connexion with other tissues to which it is attached, as when all the coats of the bowels slough in strangulated hernia. When it does mortify, it becomes black, of a soft, almost pulpy consistence, and excessively fetid; imparting, however small the extent of the gangrene, the same fetid odour to the liquid effused into the serous cavity, in which also it produces an evolution of offensive gases. When false membrane exists, it sometimes participates in the affection, presenting the same phenomena as the proper serous tissue.

The fibrous tissue is among those in which gangrene is established with the greatest difficulty. This is especially true of tendon. Nevertheless, these structures do occasionally undergo mortification. Their appearance is at first little altered; and it is sometimes difficult to decide, by the colour alone, whether they are dead or living, until the appearance of a red line of inflammation indicates the limits of the gangrene. But, when long dead, or when the mortification is of slow occurrence, they lose their shining appearance, become grayish or of a dirty yellowish or ash colour, and soften so that they may be torn, though they are longer in separating than most other parts.

The skin is more liable to gangrene than any other tissue, unless it may be the areolar. The appearances which it presents, immediately before the death of the part, have been already described. (See page 34.) After mortification has taken place, the surface, if moist, is of a grayish or ash colour; if dry, is darker and even blackish. When the gangrene has resulted from excessive cold, or sudden violence, the colour is at first often white or yellowish, and ultimately assumes a darker hue. The affected portion of skin is usually soft, though somewhat consistent; if the mortification has occurred during suppuration, it is still softer; and, if the subcutaneous cellular tissue has been at the same time inflamed, it is converted into a grayish pulp, and mingles with the ichorous pus from the parts beneath. In dry gangrene the skin is dry and shrunk.

In mucous tissue, which is occasionally, though not very frequently, the seat of gangrene, the mortified part is fetid and very soft, so that it may be readily removed by scraping with the back of a scalpel from the subjacent structure. The colour is sometimes white at first, but is ultimately gray, slate-coloured, or blackish. When the gangrene is consequent upon inflammation, the neighbouring parts are usually of a livid redness, very soft, and considerably swollen from the infiltration of a fetid, bloody, serous fluid.

In the glandular tissue, gangrene is not frequent, and, when it occurs, presents the ordinary appearances which characterize the affection. In the bloodvessels, it is exceedingly rare as an original affection, the vascular tissue having an extraordinary power of resisting mortification, and often remaining sound in the midst of a mass of gangrene. Little is known of the affection in the absorbents, though the lymphatic glands occasionally undergo mortification. Muscles, in a state of gangrene, are usually of a dark livid colour, though sometimes, when not exposed to the air, they are yellowish or grayish, and are black in dry gangrene. Gendrin states that gangrenous eschars of the heart are blackish or greenish. Mortification is very uncommon in nerves, unless when pervading the whole structure of which they form a part. It occasionally occurs in the brain, though rarely. In this structure, the gangrenous part is

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gray or blackish, very soft, and very fetid. But fetor and softening are not certain signs of mortification; for the latter is often produced by inflammation, and the former may occur from the decomposition of the pus, when from any cause, as in cases of external violence, air has admission to the part. In bones, gangrene is not unfrequent, and is perhaps produced more readily by an equal amount of cause than in any other tissue. The mortification of bones is attended with phenomena somewhat peculiar, which have given it a distinct name, and have led to especial attention. It is usually denominated necrosis. Of this affection, however, as it is considered as falling within the province of the surgeon, I shall not treat in this place. It is sufficient to say that it may occur as a result of inflammation which the feeble vitality of the tissue is unable to resist, or from direct depression through the agency of cold or an interrupted supply of blood, as when the periosteum or medullary membrane, upon which its nourishment depends, is separated from the bone or destroyed. The dead portion of the bone is separated by ulcerative absorption, and through the same agency is ultimately discharged, if the patient do not sink during the process. The mode of separation is highly interesting, and affords a beautiful illustration of the resources of the system; but the reader is referred to works on surgery.

The effects upon the system produced by gangrene, when extensive or internal, especially when it affects a vital organ, are very striking. The pulse is very feeble and frequent, and often irregular; the skin is pale or of a sallow tinge, and is bathed in a cold clammy sweat; the respiration is disordered; the features are sunken, with an expression of wildness or great anxiety, though no pain may be felt, and the sudden cessation of any pre-existing pain is considered as an evidence of commencing mortification; there is usually great thirst, and frequently more or less nausea and vomiting; the abdomen is often tympanitic; and great disorder of the nervous system is evinced by subsultus tendinum, singultus, deranged sensations of various kinds, and even delirium. But these symptoms, which, occurring in the last stage of inflam mation, and especially when attended with a sudden cessation of pain, were formerly very commonly considered as certain proofs of mortification, are now known frequently to take place in cases which exhibit no appearances of gangrene after death. The probability, however, is that, in many of these cases, gangrene is not discovered only because the patient sinks under the disease before the local affection has had time to run into absolute mortification; and that, in others, though death may have occurred in the part, yet general death has so speedily followed, that no time has been allowed for the commencement of putrefaction, which, as before observed, is the only unequivocal sign of gangrene.

Article IV.

CONGESTION.

THIS may be defined to be an unhealthy accumulation of blood in the blood-vessels of any part of the body. It often has its origin and chief seat in the capillaries; but it may extend also to the arterial and venous ramifications, and even to the larger trunks. It is considered by some writers as of primary importance in disease; but it is always an effect of some pre-existing morbid state or action; and it is a partial view which is directed to this effect alone, without embracing the other elements that enter into the complex phenomena presented by the part congested. There is probably no