A bland pus is usually in a state of beginning putrescence, so that it is only relatively bland, and acquires extreme virulence when long exposed to putrefactive agencies. It is possible that those agencies producing an ichorous pus are the same or different from those present in bland pus. The ichorous exudation contains less corpuscles than bland pus, is more fluid, less opaque, strongly alkaline, of a greenish color, and of offensive odor.
In hemorrhagic inflammation the exudation contains large numbers of red blood-corpuscles. The occurrence of this form is sometimes associated with peculiarities of the cause, as is obvious from the epidemics of hemorrhagic small-pox, measles, scarlatina, and cerebro-spinal meningitis. It is also associated with peculiarities of the individual, as in such epidemics all cases are not equally hemorrhagic, and in scurvy the hemorrhages are attributable to the abnormal conditions to which the sufferers are exposed. Hemorrhagic exudations are also met with in those inflammations of serous surfaces accompanying the outcropping of tubercular and cancerous or sarcomatous growths. In all cases a hemorrhagic exudation represents a grave complication, and when found in serous cavities has a certain diagnostic, as well as prognostic, importance.
Fibrinous inflammations are characterized by the presence in the exudation of considerable quantities of fibrin. As the prevailing theory of the formation of fibrin demands fibrino-plastic as well as fibrinogenous material, both are to be sought for in the exudation. The latter is present in the liquid portion of the exudation; the existence of the former, as well as that of the ferment, is dependent upon the presence of the white blood-corpuscles. The more numerous these, within certain limits, the more abundant the formation of fibrin. As their death appears essential for the fibrinous coagulation, the latter is most constantly met with in those parts of the body where the white blood-corpuscles are quickest separated from influences favoring their life. The farther removed they are from the blood-vessels, the more likely is their early death. Fibrinous exudations are therefore frequent and abundant in cellular and serous (sero-cellular) inflammation of the great serous cavities of the body. The clotted fibrin appears as false membrane lying upon the serous surface, either smooth or rough, tripe-like, or as villosities projecting above the surface, and again as bands, fibrinous adhesions, stretching across the cavity and uniting opposed surfaces.
The frequent occurrence of fibrinous exudations on the mucous membranes of the larynx and trachea, accompanied by the suffocative symptoms known as croup, has led to the use of the term croupous inflammation as synonymous with fibrinous inflammation, and its application to various parts of the body where croupous—i.e. suffocative—symptoms are not in question. Croupous inflammation, when used, is to be considered as an anatomical term, indicating merely the production of fibrin, and, for the avoidance of confusion, it is preferable to substitute fibrinous for croupous when such inflammations are described.
The disease, croup, it is well known, may exist without a croupous—that is, fibrinous—inflammation, as is familiarly recognized in the constant use of the terms spasmodic, membranous, and diphtheritic croup.
Fibrinous inflammation of the mucous membrane of the larger air-passages is much more frequently met with than that of mucous membranes elsewhere, as of the intestines, uterus, and bladder. The pseudo-membranous inflammations of the latter tracts are more commonly the result of the catarrhal and diphtheritic varieties than of the fibrinous form. Fibrinous exudations on mucous surfaces, according to Weigert, can only take place when the epithelium is destroyed. Hence those causes which give rise to the destruction or detachment of the epithelium are alone capable of producing a fibrinous inflammation of mucous membranes, and a fibrinous laryngitis, trachitis, and bronchitis may result from the local application of such irritants as steam or ammonia, as well as occur in the diseases croup and diphtheria.
Fibrinous exudations may also be present within tissues, especially in those whose meshes are wide, provided the essential elements of coagulation are present. The coagulative necrosis of various organs, to be more fully mentioned hereafter, is closely allied to fibrinous clotting, the fibrino-plastic element being derived from the death of the parenchymatous cells of the part.
In the existence of a fibrinous pneumonia the conditions are somewhat analogous to those present in the fibrinous inflammation of serous surfaces and of the areolar connective tissue. There is present an abundantly cellular exudation, held in the place of its origin, the cells undergoing rapid death and surrounded by a wall whose superficial cells resemble in structure, if not in origin, the endothelial cells lining the smaller lymph-spaces of connective tissue, as well as the larger cavities within the same, known as serous cavities.
The diphtheritic inflammation is no more to be confounded with the disease diphtheria than is the fibrinous inflammation with the disease croup. Although diphtheria owes its name to the frequent presence of an apparent membrane, it may be said that the latter is not essential to the existence of the former. Diphtheria, like croup, is an affection in which various exudations may be present, and the anatomical product alone does not suffice in all instances for the recognition of the disease. In croup there may be a swollen mucous membrane, with a slight superficial mucous exudation, or a more abundant exudation of desquamated epithelium and mucus, as well as a fibrinous false membrane. In diphtheria the same varieties of exudation may occur, and in addition the diphtheritic exudation may also be present. The latter, however, is not limited to the disease diphtheria, for its presence is apparent in other mucous membranes than that of the air-passages, and in the pharyngeal mucous membrane in other diseases than diphtheria. A diphtheritic conjunctivitis, enteritis, cystitis, and endometritis are recognized. The cutaneous surfaces of the body may also furnish a diphtheritic exudation. The diphtheritic inflammations of wounds and of variolous eruptions are instances in point.
The characteristics of a diphtheritic inflammation are the presence within the tissues of a clotted exudation, which is associated with a defined swelling and death of the part. The exudation contains not only dead leucocytes and interlacing fibres, but is also provided with abundant granular material, much of which presents the well-known peculiarities of microscopic organisms. The apparent false membrane is thus dead, infiltrated tissue, which may be torn away from the continuous unaffected tissue, leaving a raw, rough surface, but not peeled from a comparatively smooth surface, as in other forms of pseudo-membranous inflammation.