In some cases, owing to the character of the inflammatory process, there may have been no such destruction of tissue as to necessitate filling up of gaps, but yet, as the result of the irritation, new growth has gone on within the irritated area. In such cases, when the inflammatory process has ceased, the area re mains thickened, and more dense than normal. Such thickenings may persist; but also they may in course of time gradually lessen by de generation and absorption of much of the new material, In such cases the new growth does not occur in hands, or patches, or masses, but is rather infiltrated, as the phrase is, diffused within the whole area where the inflammation existed.
But again, the irritation may be so intense that the white cells that flock from the dilated blood-vessels to the seat of irritation fall vic tims to the attack and become transformed into matter, pus, as it is called, while also the elements of the attacked tissue are de stroyed by the irritation. This is called sup puration. If this occurs on the surface of the body, then a breach is made in the surface, and what is called an ulcer is the result, the yellow or dirty discharge from which consists of the destroyed elements of the tissue and of the multitudes also of white cells that have poured from the dilated vessels, mixed with the fluid that has exuded from the vessels.
This ulcer must be distinguished from what is formed, if by an injury a piece of the surface has been removed so as to expose the moist tissue beneath. On this raw surface a scab forms. This scab is formed by material oozing from the injured vessels—if it is seen unmixed with blood it is of a transparent straw colour aud of white cells from the vessels, which be tween them form on the raw surface a clot or coagulum, which later dries and forms a scab. Of course as this fluid wells up on the raw sur face it will mix with any dirt or discoloured material it comes into contact with, but it is itself clear and pure to begin with. Under the protection it offers to the raw surface, healing goes on rapidly, so that when the scab drops off the wound is whole—if it has not meantime become infected.
But to return. If the irritation has been so intense as to destroy the elements of the tissue attacked, as well as the white cells that have hurried to the rescue, pus or matter is formed. Now, if this occurs, not on the surface, but in the depth of a tissue, then in the place which marks the centre of the irritated region the elements of the attacked tissue have been de stroyed and transformed, with the white cells and exuded fluid from the blood-vessels, into a semifluid yellowish mass—dead material. This material occupies, as it were, a cavity in the inflamed tissue. But if one could study what is going on ill the tissue, one would find it is not by any means inactive. In the heart of the fray death and destruction have been wrought, but the field is not therefore lost. All round the outskirts of this dead fluid-mass the same processes are going oil that have been described already. There is, all round, a zone in which blood-vessels are dilated, white cells are pour ing from them and multiplying, and the tissue cells of this zone are also proliferating. If it
is in a situation where one's finger can feel it, this zone is marked to the touch as one of in creased density and thickness. Indeed, by the inflammatory processes described, a wall is being hastily thrown up all round the central mass of dead stuff, a wall which, to begin with, shuts it off from the as yet unattacked region beyond and limits its power to hurt, and, to end with, will gradually broaden and thicken and so encroach on the dead centre till it crowds it into the smallest possible apace.
Now the process by which the matter or pus has been formed is called suppuration, as has been already said, but the collection of matter so formed is called an abscess. If the abscess has formed somewhere on the external part of the body, it will probably show as an elevation of the surface, and if a finger of each hand be placed on the elevation, one on each side, and if the swelling be pressed first by one finger and then by the other, the matter will be displaced, as it would be if one were to press in the same way on any bag of fluid. The finger perceives this movement of fluid, which is called fluctua tion, and so one distinguishes between a solid swelling and a swelling due to fluid.
Now it will be clear that if this fluid be per mitted to escape, by means of a clean incision, then the process of regeneration going ou all sound in the active zone will get free play to invade the cavity, which will become speedily filled up by the new rapidly-growing tissue, and the destruction will be repaired. If one could look into such an abscess cavity, from which the matter had been removed, the new tissue would be seen as little firm red elevations all round the healing margin. These elevations consist of round cells and loops of fine blood-vessels, and they grow with marvellous rapidity, filling up even large cavities in a very short time. It is called granulation tissue, because of the granular appearance the growing margin pre sents. But this tissue is ultimately converted into the fine fibrous scar tissue already de scribed.
In unhealthy persons or depressed constitu tions the zone of healthy growing new tissue round the abscess may be poor and weakly. Thus the suppurating process may not be cir cumscribed, but may spread and work its way through extensive areas of the attacked region.
The worse degree of irritation is that in which the irritant is so powerful or so ex tensive that masses of tissue are killed at once, before reaction has time to occur. Pieces of tissue which die and separate in mass are called sloughs, and when a piece of tissue dies in its whole thickness it is said to become gangrenous. But round the circumference of the slough or piece of gangrene the same changes occur that have been so fully de scribed as characteristic of inflammation, the purpose of which is first to protect the still living tissue, and second to separate the dead from the living and ultimately cast it off.