A grayish, yellowish-gray, or if containing blood-corpuscles, even red, reddish-gray exudate which, in great part, speedily solidifies, into bulky, membranaceous, plug-like, or frame-like coagula, whilst the remainder, where the proportion of blood-serum is considerable, coagulates in the latter into flocculi, thus parting into a solid and a fluid constituent. It presents itself, on a closer inspection, as a clodded, fibrous, diaphanous blastema, of very tenacious properties, the broken surface of which is felt-like and studded with nuclei and nucleated cells. It answers to fibrin 2. It is observed in its purest form in wounds, when these agglutinate and heal by the first intention. Besides this, it occurs upon the pleura, in areolar tissue, in muscles, in bones, upon the endocardium and the internal bloodvessel membrane, in the brain, occasionally, as pneumonia, in the parenchyma of the lung, which either slowly recovers its natural state through absorption, or ends in induration with extinction of the pulmonary texture. Upon serous membranes it constitutes the peripherous coagula lining the inner surface of serous sacs. It frequently enters, in common with a certain proportion of normally constituted fibrin, into the composition of other exudates, as that portion of them upon which a change of texture depends, for example, into the croupous, the purulent, etc.

The following are its metamorphoses, the most remarkable amongst which is its textural conversion.

(a.) It becomes partially or wholly reabsorbed; this occurs slowly, through the instrumentality partly of the serous portion of the exudation itself, partly of a supplementary effusion of serum, succeeding to the resolution of the stasis. These humors furnish the solvent - the corroding media, so to speak, for the solidified fibrin effused, having incorporated which, layer by layer, either in solution, or in a state of minute subdivision, they forthwith become reabsorbed. In like manner, the fibrinous coagula within the vascular system; for example, vegetations, thrombi, etc, are progressively taken up again into the blood.

(b.) It wastes and hardens, with the loss of its fluid part and with lessening of its volume, to a horny, and eventually, perhaps, to an ossified mass.

(r.) It undergoes a change of texture, commonly, and for the greater part, consisting in an ulterior development of that fibrillation of the blastema which ensues upon the solidifying of the exudate. To avoid repetition, we refer for the details of this process to the heads - New Growth of Areolar Tissue, and Fibroid Formations.

In rare instances, the new formation of bloodvessels is predominant therein, more especially in exudates upon the arachnoid membrane. In the vicinity of serous membranes, there result serous layers, a new serous sac; in contiguity with bone, bony texture.

The time requisite for these transformations is scarcely definable in a general way. Under favorable circumstances, they are wont, even in voluminous exudates, to attain an advanced or nearly completed state, within the space of six weeks.

The constitution of the exudate corresponds, as before stated, with that of fibrin 2, having either been acquired in the stasis or pre-existed as a blood crase. It is a quantitative anomaly consisting in an exaggeration of the formative processes which occur in normal plasma, - and especially in the locally and generally increased generation of a fibrin (hyperinosis) marked by its coagulable and plastic properties.