The small round white cells (lymphocytes) and the eosinophile leucocytes take no prominent part in phagocytosis.
EXUDATION.
In inflamed vascular tissues one of the most important results is the exudation. This is not, however, a mere transudation of the liquid parts of the blood, as takes place in dropsy, but it is to a large extent a selective process determined apparently by the condition of the capillary walls, and the nature of the inflammation is stated according to the character of the exudate. The dropsical effusion contains little albumen, fibrine or cell forms, and does not coagulate. The inflammation exudate contains abundance of fibrine, cells and other solids and coagulates spontaneously in contact with inflamed tissue, or when removed from the body, by reason of the transforming leucocytes. Inflammatory exudate usually contains 6 to 8 per cent. of solids whereas the normal canine lymph contains 4 to 6. The exudate varies not only in different inflammations, but in successive stages of the same inflammation. The exudate may be mucous, serous, fibrinous or hæmorrhagic.
Mucous Exudate. In inflammation on a mucous or synovial surface the inflammatory exudation, mingled with the more or less altered secretion of the mucous glands, and the epithelial cells and leucocytes forms a viscid fluid, rich in mucin, and characterizing the mucous or catarrhal inflammation. The nature of the discharge varies greatly, the serous character predominating at the start of the inflammation, and a thick, opaque creamy or semi-solid muco-purulent material appearing as the disease advances. It contains filaments of precipitated mucin insoluble in acetic acid or alcohol and cells in all stages of change from the exudation leucocyte and mucous cell to the pus corpuscle, the latter being characterized by its bipartite or tripartite nucleus rendered visible by contact with weak acetic acid.
Serous Exudate. This consists of the liquid elements of the blood with only a limited amount of fibrine formers and consequently little tendency to clot firmly. The presence of fibrinogen however serves to distinguish it from the liquid of mechanical dropsy, as does also the greater quantity of cells and nuclei of common salt and phosphates. It is usually straw colored in mass, but is sometimes slightly opalescent by reason of the numbers of cells and floating filaments of fibrine. Serous exudations take place in the early stages of inflammations (as in catarrh) and in inflammations of serous membranes (pleura, peritoneum, joints), in strong, vigorous subjects. They constitute the liquid contents of blisters whether raised by medicinal irritants, chafing, or heat. They clot under heat and nitric acid with a firmness proportionate to the amount of albumen.
These effusions are dangerous by reason of their interference with the functions of organs by pressure as with the dilatation of the lungs, the movements of the heart, the action of joints, or the integrity of the brain or spinal cord. When the causative disease has subsided they are usually speedily reabsorbed, the cells passing into the lymph vessels, or becoming degenerated, liquefied, and absorbed. Yet serous effusions often remain as permanent accumulations. For the blood staining of serous effusions and their clearing up, see under pleurisy.
Fibrinous Exudate. This is characterized by the amount of fibrinogen and fibro-plastin in its composition and by the comparative absence of leucocytes. It oozes through the vessels and coagulates in the tissues or on the surface of inflamed serous or mucous membranes. The more liquid part separating from the coagulum escapes from the free surface or accumulates in the lower part of the serous cavity. The coagulation is doubtless caused by the fibrine ferment derived from the rapidly proliferating cells and degenerating leucocytes. It usually occurs promptly in or on an inflamed tissue, but in contact with healthy structures only (as in a serous sac) it may remain fluid for an indefinite length of time. This exudate constitutes the false membranes that form on the pleura, pericardium or arachnoid, the coagulum of fibrinous pneumonia, and the plastic lymph on the surface of a granulating wound. It is especially injurious by reason of its enveloping organs (lungs, heart, bowels, iris) and subjecting to permanent compression by reason of its contracting, also by binding them to adjacent structures by false membranes. In coagulating it becomes first fibrillar then granular and finally undergoes molecular degeneration (Cornil and Remvier), or development into new tissue (Paget). When organized it usually takes the form of the adjacent tissue from which its trophic cells are derived. Thus in divided tendons, in serous membranes and in granulating wounds it is fibrous, and between the ends of a broken bone it is osseous. If however, the adjoining tissue is a highly organized one, like nerve or muscle it may be replaced by a simpler (fibrous, osseous).
Fibrinous inflammations are especially found in connection with inflamed fibrous tissues and in strong vigorous subjects.
Blood Exudations. In all inflammations there is some migration of blood globules (red as well as white) but seldom in quantity sufficient to stain the tissues materially. Minute ruptures of the capillary vessels are not uncommon, with punctiform clots in the tissues, but extensive escape of blood is mainly seen in penetrating or contused wounds of the loose, subcutaneous connective tissue, and in infective inflammations (anthrax, Rinderpest, swine plague, petechial fever, malignant catarrh, snakebites) with destruction of blood globules or extreme changes in the walls of the capillaries. Newly formed vessels in friable neoplasm are subject to blood effusions. In acute inflammations of serous membranes the exudate is usually of a dark port wine hue at first. In such cases it may pass in succession through all the stages of dark red, brick red, yellow, reddish, and chocolate color, before becoming milky and finally transparent.
Croupous Exudate. Croupous inflammation usually occurs on or near a mucous surface and is characterized by an exudation consisting mainly of fibrinous material entangling white cells, epithelium, a few pus corpuscles and some form of bacteria. In true diphtheria of children this is the Löffler bacillus, in the pseudodiphtheria, attending on scarlatina, etc., it is streptococcus pyogenus, in the diphtheria of calves it is bacillus diphtheriæ vitulorum, and in that of chickens and pigeons it is the bacillus diphtheriæ columbarum (Löffler). Pseudo-membranous inflammations therefore constitute a group agreeing in the nature of the exudate but differing essentially in the cause. This difference in the cause has a most material effect on the course and gravity of the disease. One form like true diphtheria in man not only extends into the tissues, and tends to necrotic changes, but also poisons the nerve centres by the toxic materials absorbed inducing troublesome paralysis, while another like croup of children establishes a violent but essentially superficial disease and when that recovers it leaves no ulterior ill effects elsewhere.