A "transudate" is a liquid having a composition resembling that of blood-serum, while the term "exudate" is applied to an effused liquid whose composition approaches that of the blood-plasma in the relationship of its solid and liquid parts, besides in most cases containing numbers of colourless blood-corpuscles.
The addition of some of the liquid squeezed out from a blood-clot, of the squeezed blood-clot itself, or of a little blood-serum, is sufficient to throw down a fibrinous coagulum (Buchanan), evidently by these substances supplying the fibrin-ferment.
The proteid constituents are very much like those of blood-serum, although they never come up to them in amount (Runeberg).
To mention examples, blood serum solidified at a suitable temperature is a highly suitable medium, and various media are made with extract of meat as a basis, with the addition of gelatine or agar as solidifying agents and of non-coagulable proteids (commercial " pep tone ") to make up for proteids lost by coagulation in the preparation.
It is, however, also accompanied by the appearance of certain bodies in the blood serum of the animal treated, to which the name of anti-substances is given, and these have been the subject of extensive study.
