This section focuses on the microscopic evaluation of fluids accumulated in body cavities: cerebrospinal, pleural, pericardial, and peritoneal (ascites). Synovial fluids are described below under “Other Body Fluids.” Aspiration followed by chemical, microscopic, cytologic, microbiologic, and, if indicated, flow cytometry examinations should help determine the etiology of accumulated pathologic fluids by providing important information regarding infection, hemorrhage, inflammation, or malignant infiltration. Total cell counts are performed using undiluted (or in the case of very high counts, diluted) body fluids with a hemocytometer. Differential counts are done using a smear following centrifugation (Cytospin) and staining with Wright-Giemsa stain. Bacterial identification and cultures and the chemistry of body fluids are described separately.