Exudate

EXUDATE, effusion, a fluid that exudes from small vessels (capillaries, venules, arterioles) during inflammation. Only in rare cases is the E. completely transparent (serous E.); usually it contains admixtures of various cells, some originating from local tissue (desquamated epithelium, free mesenchymal cells), and some exiting the vessels in the so-called process of emigration (leukocytes, lymphocytes) or diapedesis (erythrocytes). Depending on the content of various types of cells or protein fractions in the E., one speaks of serous, purulent, hemorrhagic, fibrinous, etc., E. (see Inflammation). The specific gravity of the E. is always significant: 1.018-1.022 and higher (up to 1.040 in purulent inflammation). In this way, the E. differs from transudate (see). It should be noted, however, that there cannot be an absolute opposition between the latter and the E.: both in physical properties (color, transparency, specific gravity) and in protein composition, transudate is often indistinguishable from E. Such, for example, is the edema fluid in nephritics, certain types of ascites in liver cirrhosis, etc. To distinguish between one and the other, it is recommended to study the entire process as a whole, taking into account all the clinical and morphological phenomena that accompanied this or that process. For a more precise determination of the nature of the E. and the process that caused it, microscopic and bacteriological examination of the corresponding fluid is performed. Microscopic examination of sediments from the E. is carried out either in an unstained state (under a coverslip) or by staining the corresponding smears, for example with methylene blue, according to Giemsa, etc. Bacterioscopic and bacteriological examination is carried out following the usual rules for such examination (smears, seeding on media, inoculation into animals, etc.).