Serous effusions are, generally speaking, either merely serous (blood-serum); or again from their containing a larger proportion of albumen, albumino-serous; or, lastly, owing to an admixture of fibrin, fibrino-serous. This gives rise to several important distinctions in their physical bearings. The mere serous effusion is a thin, watery, limpid, colorless, or pale yellowish, now and then reddish-yellow fluid, salt to the taste, and containing little, if any, albumen. A large proportion of albumen renders it tenacious, like a thin synovia. An admixture of fibrin manifests itself upon serous membranes as a peripherous coagulum of inconsiderable thickness, as a villous deposit, as a filamentous, wide-meshed, network or finely membraned honeycomb, or as a flocculent cloud within the serous fluid. Or again, it may, in the shape of the so-called spurious fibrin, which solidifies tardily, perhaps only after cooling and coming in contact with the air, appear in the effused serum as soft, jelly-like, transparent, coagulate pellets, which are often found lodged within the aforesaid true fibrinous network, or honeycombed structure. Fibrino-serous effusion may be said to be invariably the product of an inflammatory stasis. It is simply fibrin-exudate, with a notable preponderance of serum. It might well be denominated fibrinated dropsy.

Albumino-serous effusion is sometimes, like that previously described, the product of a not very intense, often of a protracted, stasis or simple congestion. As an example, may be cited the (inflammatory) oedema, encompassing the range of an inflammation. It occurs more commonly independent of the latter, in the albumino-serous crasis, as general oedema.

Mere serous effusion is the result of an excess of serum in the blood - the serous crasis; or else it is the product of acute and more frequently of chronic hypersemia. In the latter case, the effusion seems to originate less from the capillaries than from the small thin-membraned veins.

It represents genuine dropsy, and does not at all imply a foregone inflammatory stasis.

Serous effusion, as such, is not organizable. Albumen and fibrin, however, when blended with it in sufficient quantity, are susceptible of a somewhat tardy, structural change. It relaxes and tumefies the textures on becoming imbibed, destroys their contractility, and by long-continued contact exerts, more especially upon the muscular fibres, a remarkable power-bereaving influence.

4. Purulent And Ichorous Effusion

These range immediately with fibrinous and albuminous exudation, as also with their fibrino-serous, albumino-serous combinations. Purulent effusion seems, however, to be more especially akin to the fibrino-croupous exudate.

The importance of these products renders it desirable to discuss them at greater length.