Croupous Exudation has several varieties, dependent upon a qualitative impairment of the fibrin. It is, with the utmost impropriety, confounded with the former and its kindred crases. It is marked by a high degree of coagulability; by a yellow, or greenish-yellow coloration; by its opacity; by its inorganizable nature; by its early tendency to break down, to liquefy; frequently by a corrosive, texture-softening power. The quantity of serum simultaneously thrown out is relatively insignificant.

The croupous process of exudation and its product are further distinguished,

1. By the commonly excessive, exhausting, quantity of the exudate, and its extension over wide ranges of organs and textures.

2. By the rapidity with which the effusion is brought about, where the stasis depends upon a pre-existent crasis.

3. By the often slight vascularity of the diseased texture; a circumstance due, it may be, to the blood-corpuscles not appearing prominently in the opaque, over vigorous plasma, or else to the exudate, by its excessive quantity, soon leaving the bloodvessels exsanguine and collapsed.

4. By less adhesiveness.

5. By considerable fattiness of the exudate.

The principal metamorphosis of the croupous exudate is the aforesaid breaking down, and liquefying to a fluid more or less analogous to pus, which constitutes the so-called liquid, purulent exudate.

This metamorphosis first of all affects the solidified blastema intervening between certain form-elements of the exudate; only in an adherent portion of organizable fibrin does the latter undergo a change of texture - namely, to areolar tissue. When liquefied, it may be wholly reabsorbed, or may leave a residue in the shape of a fatty, curd-like, cretaceous pap, or, lastly, of a glutinous fluid, abounding in free fat and in salts of lime (in elementary granules, granulated cells, cholesterine crystals), which speedily thickens into a cretaceous concrement.

(a.) Croupous Exudation, an abundant, proportionately to its contents in blood-globules or in blood-pigment, more or less red (red hepatization of lung), or grayish-yellow mingling with green, opaque exudate, consisting of a sod-like, fibro-laminated, or striated membranous basement, a large proportion of dotted substance, nucleated formations, dull granulated nuclei and nucleated cells. The nuclei are not influenced by acetic acid, beyond some little shrivelling, together with a sharpening of their contours. This answers to the constitution of fibrin 3. It liquefies first in its basement mass, with change of texture of any adherent portion of organizable fibrin, to a pus-like fluid.