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.
A =Chyliform exudate= has been noted in peritonitis in the dog the milky
whiteness being due to fatty granules.