phenomena, the simplest result is the effusion of fibrinous matter, or organizable lymph, into the substance of the part inflamed, or upon the nearest free surface; and thus is produced a condensation of the tissue, or a new growth upon the membrane. But when the depression of vitality is more complete, the tissue at that spot gradually dies and disintegrates; and whilst itself undergoing such changes, it gives origin to similar changes in the effused fibrine, which it converts from a plastic or organizable deposit, into an aplastic or unorganizable one, namely, pus, the cells of which degenerate without passing into any higher or more permanent form of tissue, whilst the liquid through which they are dispersed has lost its coagulating power. Thus is produced the Suppurating process; which may either take place in a cavity thus excavated in the substance of a tissue or organ; or on a free surface. In either case, the surrounding tissues, which are less inflamed, and in which the vitality is impaired but not destroyed, become consolidated by a deposition of organizable fibrine, which prevents the infiltration of pus through their substance. If this should not occur, through a want of power to generate well-elaborated fibrine, the suppurating process extends itself rapidly, with the most calamitous results; the properties of pus being such, as to produce a tendency to decomposition, both in the blood, and in the solid tissues into the substance of which it may be carried.

633. Another consequence of Inflammation is Ulceration, which is a breach of surface caused by the same process as that which forms the cavity of an abscess,-namely, the degeneration of the inflamed tissue, and the removal of its particles, either by absorption, or by solution and ejection in pus. Many ulcers commence as abscesses near the surface, which at last come to open upon it; and others are preceded by inflammation of the superficial tissues, which die and are thrown off, leaving a vacuity, which may be subsequently increased by the extension of the degeneration of the deeper parts. These may either die and be thrown off en masse, constituting what is known as the "sloughing ulcer," or they may disintegrate more slowly, and may be dissolved in the discharge from the ulcerated surface. This discharge, when proceeding from a spreading ulcer, is usually of a thin ichorous quality, and has the power of exciting unhealthy action even in healthy parts to which it may be applied; and it is its change to what has been designated as "laudable pus," that indicates the cessation of the destructive, and the commencement of the reparative process (§ 636).

634. The state of Gangrene, which consists in the entire loss of vitality of the part, with a complete cessation of the circulation through it, is commonly regarded as a result of Inflammation, when this process occurs in its most intense form; but it may be more rightly considered as the ultimate consequence of the causes which produce Inflammation. For it is an essential part, as we have seen, of the condition of Inflammation, that the vitality of the affected tissues should be lowered; and thus there is in them always a tendency to death, which is most completely developed in Gangrene. We have a well-marked example of this complete destruction of the life of a part, by the intense operation

of causes, which, when less potent, occasion Inflammation, in the case of frost-bites produced by Cold; for this agent at the same time produces contraction of the blood-vessels, and depression of the vital powers of the solid tissues, proceeding to the complete destruction of them; whilst in the parts adjoining those which are actually killed, the inflammatory state is developed, an effusion of fibrine being produced, which serves to plug up the mouths of the vessels, and thus to prevent hemorrhage, when the mortified part drops off. Here we see, that the violent action of cold completely destroys the vitality of the part most exposed to it; and this by its direct influence on the properties of the organized structure. No inflammation can take place in the part thus killed, because the vital processes are altogether brought to an end. But inflammation takes place in the adjoining parts, which are less seriously affected; for the depression of their vital powers occasions the result already adverted to,-namely, the production of an increased amount of fibrine in the blood, and an infiltration of this substance into their tissues. The same is the case, with regard to the operation of other powerful agents; such as those which (like Caustic Potass, or Sulphuric Acid) destroy the vitality of the parts to which they are applied, by the chemical decomposition of their tissues. The Inflammatory process is set up, not in the parts which are killed by the application, but in the surrounding tissues, whose vitality has been simply depressed; and thus, when the slough, or dead part, is cast off, there is a preparation for the development of new tissue to supply its place, from the superabundant plastic materials of the surrounding parts.

635. If, then, we limit the term Inflammation, as there seems reason to do, to that state, in which there is a tendency to stagnated circulation, with increased production of Fibrine, in the vessels of the part, we see that the Gangrene cannot be a result of that process, which is one rather of reparation than of destruction. But Gangrene proceeds, where we can distinctly trace its causes, from the violent operation of the same agents, as those which, in a less degree, produce Inflammation. And where this last process is not set up at the line of demarcation between the living and the dead parts, Gangrene, like Suppuration, has a tendency to spread; the influence of the decay, which is taking place in one part, having a tendency to propagate itself, to the adjoining tissue; and a constantly-extending destruction being thus produced.

636. We have now to speak of those reparative processes, by which the effects of disease or injuries are more or less perfectly recovered from. The healing of a simple wound may take place by the direct adhesion of its walls, when they can be drawn closely together; but more frequently it is accomplished by the intermediation of a thin layer of "coagulable lymph," which may be thrown out for the purpose of reparation, without the existence of inflammatory action. But the reparation of wounds, in which there has been so great a loss of substance that neither direct nor indirect adhesion can take place, is accomplished by the gradual development of new tissue from the "nucleated blastema" with which the cavity is first filled. This, however, inay occur in two very different modes; and from the inquiries of Mr. Paget it appears that the determination of one or the other

of them is chiefly dependent on the condition of the wound, as to seclusion from air, or exposure to it. When the reparative effusion is poured out into a subcutaneous wound, the "nucleated blastema" appears to be gradually developed into fibrous tissue without any loss, and usually with freedom from local inflammation (beyond what may be the immediate result of the injury), as well as from constitutional irritation. This process seems to take place naturally in cold-blooded animals, even in superficial wounds; the contact of air not producing that disturbance in it, which it occasions in warm-blooded animals. And Nature frequently endeavors (so to speak) to bring it about in the superficial wounds of warm-blooded animals, by the formation of a large scab, which protects the exposed surface; but this happens much less frequently in the Human subject, than it does among the lower animals; the unnatural conditions in which a large proportion of the more civilized races habitually live (especially deficient purity of the air, continual excess in diet, and the frequent abuse of stimulants), being obviously unfavorable to it. The application of steam to wounded surfaces has been found to favor the reparation by the most healthy process; and the formation of an artificial scab by means of resinous unguents has also been practised with advantage. It is the duty of the Surgeon to endeavor to promote it by every means in his power; since it is the method of healing, which is not merely the most desirable as regards its economy of nutritive material and freedom from constitutional irritation, but which most completely supplies the loss of substance, so that the cicatrix does not contract. The newlyformed fibrous tissue becomes vascular, by the extension of loops or arches from the adjacent capillaries, and of other loops from these; and subsequently other structures-such as bone, lymphatics, and nerves, may be developed in it. True Cartilaginous tissue, and the higher form of Muscular fibre, however, seem never to be thus generated de novo in the new tissues of a repaired part; so that wounds of Cartilages and Muscles are united by simple fibrous texture.

637. In an open wound, on the other hand, which is healing by the process termed Granulation, the "nucleated blastema" is rapidly developed into cells, amongst which vessels speedily extend themselves; but the vitality of this tissue is very low, and that part of it which is exposed to the air passes into the condition of pus, its cells being either imperfectly developed from the first, or speedily undergoing degeneration. Thus there is a constant waste of plastic material, the amount of which, in the case of an extensive suppurating sore, must be a serious drain upon the system; whilst at the same time, the local inflammation is greater, and gives rise to more or less of constitutional disturbance; and the formation of new tissue is so much less complete, that by its subsequent degeneration, and removal by absorption, a contracted cicatrix is produced, which is different from the original texture. The new tissue is here produced by a metamorphosis of cells into fibres; and this change is taking place in the deeper part of the granulation-structure, whilst the more superficial is degenerating into pus.-The difference between the two modes of reparation now described, is often one of life and death, especially in the case of large burns of the trunk in children;

for it frequently happens that the patient sinks under the great constitutional disturbance occasioned by a large suppurating surface, although he may have survived the immediate shock of the injury.

638. If the Fibrine of the Blood, however, be not well elaborated, it does not possess its due organizability; and thus instead of being converted, either when effused as an Inflammatory product, or in the ordinary Nutritive process into solid tissue, proper to the part in which it is deposited, it is liberated from the vessels in a state, which prevents any but a very imperfect structure from being developed by it, and which tends to very speedy degeneration. This is the condition of the Tubercular substance, which is so often found to replace the proper tissue, especially in the lungs; being slowly deposited there, by a sort of degradation of the regular nutritive operations; and being effused in larger quantity, when the inflammatory process is set up. There is every degree of gradation between the plastic or organizable deposit of well-elaborated Fibrine, the caco-plastic or imperfectly-organizable matter of Tubercle, and the aplastic or non-organizable matter of Pus. The microscopic examination of tubercular deposits shows, that they sometimes contain fully-developed cells and fibres, analogous to those of fibrinous exudations; but that more frequently, the cells and fibres are imperfectly formed, and are accompanied by a large quantity of a granular substance, which strongly resembles coagulated Albumen; and that in many cases, there is scarcely any trace of organization in the mass. The greatest degree of organization is found in the semi-transparent, miliary, gray, and tough yellow forms of Tubercle; the least in the opaque, crude, or yellow Tubercle. It is the opinion of some eminent Pathologists, that Tubercular matter is always deposited in the first instance in the cellular form; but that it tends to undergo a rapid and complete degeneration.

639. The constitutional state, which predisposes to this perversion of the ordinary nutritive operations, and which is known as the Tubercular Diathesis, may be the result of the continued operation of any causes, that tend to depress the vital powers; such as insufficient nutrition, habitual exposure to cold and damp, protracted mental depression, &c.; or it may be derived from the operation of the same or other causes on the ancestors of the individual, being one of those disorders which has a peculiar tendency to become hereditary. The treatment must be directed to the invigoration of the system by good food, active exercise, pure air, warm clothing, and cheerful occupations; and by the due employment of those means, at a sufficiently early period, many valuable lives may be saved, which would otherwise fall a sacrifice to Tubercular disease in the lungs, or other important organs.-Much reason has lately presented itself for the belief, that a deficiency of appropriate oleaginous constituents in the food exerts a marked influence in the production of the Tubercular diathesis. This would appear to be indicated by the very marked benefit which has been derived in the treatment of Pulmonary Consumption and other tubercular diseases, from the use of Cod-liver oil, or of other easily assimilated fish-oils. And the same view is confirmed by the remarkable exemption of the Icelanders (whose diet is extremely oleaginous) from Tubercular dis

eases, notwithstanding that the general habits of the people would seem peculiarly favorable to their production.

640. There is another remarkable class of diseases, resulting from a disordered condition of the nutritive processes;-those, namely of a malignant nature. We not unfrequently meet with abnormal growths of a fatty, cartilaginous, fibrous, or bony structure; which appear to originate in some perverted action of the part itself, and which have little tendency to reappear in the same part, when they have been removed, still less, to reappear in distant parts. But the various forms of Malignant or Cancerous disease are peculiar in this, that they are composed of cells, sometimes of a globular form (see Fig. 18), sometimes elongated or spindle-shaped, having a power of rapid multiplication, and not capable of changing into any kind of normal tissue. When a truly cancerous growth has once established itself in any part of the body, it may increase to an unlimited extent, obtaining its nourishment from the blood-vessels in its neighborhood, and destroying the surrounding parts by its pressure, as well as by drawing-off their supply of aliment. When it has developed itself to a considerable degree in one part, it is very liable to make its appearance in others, especially when the original growth has been removed; and hence the judicious surgeon is disinclined to remove a Cancerous growth of any but the most limited kind; knowing that the disease is almost certain to reappear. There is a strong analogy between such Cancerous growths, and the low forms of Fungoid Vegetation, which develope themselves in the interior of the higher Plants, and even in Animal bodies; and in both cases, the disease may be propagated by inoculation from one individual to another. But still it appears probable that Cancerous disease, like tubercular, is of constitutional origin; and the peculiar tissue which characterizes it, is perhaps to be regarded simply as the manifestation of the presence of a morbid matter in the blood, which is thus removed from the circulating current; just as fatty matter is removed by an increased formation of Adipose tissue, or as the elements of the excretions are eliminated by an increased growth of the gland-cells of which they are the appropriate pabulum.

CHAPTER VIII.

OF RESPIRATION.

1. Essential nature and Conditions of the Respiratory Process.

641. THE function of Respiration essentially consists in an interchange of oxygen and carbonic acid, between the blood of the Animal and the surrounding medium; carbonic acid being given out by the blood, and oxygen entering in its stead. It has been already noticed (§ 84) that this function is performed likewise by Plants; although, in consequence of their deriving a large part of their food from the