A Chyliform exudate has been noted in peritonitis in the dog the milky whiteness being due to fatty granules.
RESULTS AND PRODUCTS OF INFLAMMATION.
As nearly all inflammations have significant exudations it is well to follow these in their subsequent progress through reabsorption and removal, development into new tissues, necrosis, suppuration and ulceration.
Resolution. If an inflammation, slight in character and with only a moderate exudation, subsides and is followed by a rapid liquefaction of the cells and fibrinous coagula and a reabsorption of the exudate, so as to leave the part in its primary healthy condition structurally and functionally, it is said to have terminated by “resolution.” If this occurs with extraordinary rapidity it is said to have ended by “delitescence.” This is not always an unalloyed good, as often in delitescence, coagula and infecting material may be carried on by the circulation, to block the next set of capillaries in its course and set up new centres of inflammation. This is one form of “metastasis” though a more definite metastasis is in rheumatism where the disease attacks one joint today and a distant one to-morrow.
Inflammatory New Formations. Of the growths in lymph there are two principal kinds: first, the plastic, fibrinous, granular or molecular; and second, the aplastic or corpuscular. The first form tends to develop into new structure, the second to disintegrate and decay. The tendency to one or other form depends largely on the strength or weakness of the system’s health, on the deficiency or excess of corpuscles in the exuded fluid, and on the distance of the latter from living tissues and blood supply. Much also depends on the predisposition of the genus, the tendency to suppuration in lymph being in a descending series from horse, ass, and mule, through ox and sheep, to dog, pig, and finally, the bird, in which latter suppuration is quite exceptional.
Suppuration. In inflammations of a high type, in those occurring on the skin or mucous membranes in which there is an extraordinary increase of nuclei and embryonal cells, and in lymph thrown out in excess at one point, so that its central parts are far from vascular tissue and nourishment, the cell elements undergo a rapid increase and degradation into pus-corpuscles, and its solidified intercellular lymph undergoes granular decay and liquefaction into pus.
While the above conditions are favorable to the formation of pus, the process of suppuration must now be recognized as an infective process due to the propogation of bacteria (mainly chain forms—Streptococcus pyogenes—cluster groups—Staphylococcus pyogenes—and rod forms—Bacillus pyogenes). These or other bacteria are found in the pus of acute abscesses, and when absent in chronic abscesses are to be considered as having perished since the abscess was recent and active. Inoculation of a rabbit with an excess of the pus of an acute abscess produces general purulent infection (pyæmia) and early death; from a medium dose an abscess is produced; while from a small dose there is no effect whatever. In the latter case the bacteria are overcome and devoured by the abundance of vitally potent white blood globules and tissue cells. This pus-forming action of these bacteria explains the great difference in results in wounds exposed to the air and those in the interior of the body and far removed from air and its floating bacteria. A broken bone, with no wound in the skin and little injury to parts around the fracture, is readily repaired without any formation of pus, if merely kept still and immovable; whereas a broken bone, continuous with a wound through the skin, always tends to form pus or become otherwise infected, and is extremely dangerous even to life. The tendency of every open sore is to form pus on its surface but this may be arrested and avoided by preventing the access of germs, or by a free use of disinfectants and a covering which shall arrest and filter out the germs. Similarly in an abscess, evacuation followed by the injection of disinfectants, without the formation of any perceptible permanent opening to the outer air, will put a stop to the pus-formation. The subjection of an inflamed part to the control of these pus-forming bacteria is dependent on the lowered vitality and power of resistance of the inflamed tissues, and of the white cells of their circulating blood. Healthy parts can successfully resist them, though they are constantly present in surrounding air and on objects, but in this as in all other cases, of bacterial infection, so soon as the tissue is injured, inflamed and lowered in its power of vital resistance, the pyogenic bacteria assail it successfully. Hence, too, the more abundant exudations of lymph, the centres of which are farthest removed from the healthy tissues and from nourishment, are the most prone to suppuration. That the germs can make their way to such deep-seated exudations in the substance of solid tissues is to be accounted for by their gradual advance through the inflamed and weakened structures from the adjacent skin or mucous membrane, or in some instances by reason of their presence in small numbers in the blood. It is further noteworthy that those animals in which suppuration does not occur readily are such as have a special power of resistance to some other organic poisons. Thus the hog, which is supposed to be proof against snake-bite, is also, to a large extent, proof against the pus-forming bacteria.
Pus. This is a white, or yellowish white, creamy-looking product, composed of a clear, transparent fluid, rendered opaque by numerous floating pus-corpuscles. These pus-corpuscles have the same size as the white globules of the blood (¹⁄₂₅₀₀ to ¹⁄₃₀₀₀ inch) and are peculiar in that each shows within it three or more nuclei, which become visible on the addition of a drop of water or acetic acid. Each of the common embryonal cells found in the inflamed tissue usually contains two nuclei, the indication of the active increase by division into two, but when the supply of nutriment is checked the nuclei continue to divide, while the cells remain unchanged, and thus every cell comes to contain several nuclei in addition to fatty granules, and constitute pus-corpuscles.
When pus is formed in a well-maintained system and tissue, the outer layer of the lymph is developed into a fibrous sac enclosing the liquid pus and constituting an abscess. In an unhealthy system, or when the inflammation depends on some injurious poison, like that of erysipelas, this sac may not be formed, and the pus, burrowing into and between different organs, destroys the connections and substance—diffuse suppuration. When an abscess has formed in soft tissues its investing sac shrinks as it assumes the fibrous character, and the confined pus being incapable of compression, presses the membrane outward on the side in which the surrounding tissues are most loose and least resistant, hence, usually, though not always, in the direction of the skin; the soft tissues become absorbed and removed in the track of the advancing pus; and, finally, the latter reaches a free surface and escapes. Thus, an abscess usually bursts through the skin, but also, at times, through a mucous membrane into the lungs, bowels, etc., or through a serous membrane into chest, abdomen, etc. When an abscess is formed in bone or dense fibrous tissues which press equally on all sides, it may remain imprisoned for months and years after all inflammation has subsided, constituting an indolent or cold abscess. When the imprisoned pus is inclosed by thick fibrous or resistant tissues at all points but one, it will make its way along the narrow passage of yielding tissue, but as the resulting outlet is constricted, long, and tortuous, the contents cannot readily escape through it nor the walls of the abscess contract so as to expel the confined pus, and the latter goes on forming and discharging through the narrow outlet for months or years. This is a fistula or sinus.
Healing by Adhesion or First Intention. When a clean-cut wound has the blood staunched and its lips brought together without exposure to the air (or contact with pyogenic germs), they adhere at once and heal without pus or almost any appreciable formation of new tissue. Here the lymph thrown out on the cut surfaces agglutinates them, and the cells, multiplying, form a thin layer of embryonic tissue which gradually develops into a fibrous structure and repairs the breach without any perceptible scar.