With the animal in a standing position we will anesthetize an area of about 2 cm in the ventral midline and make an incision in the skin with a (No. 15) scalpel blade. Through the incision and slightly to the right of the midline to avoid the spleen, a cannula or a 18G needle is introduced until it reaches the peritoneum (see fig.1). Samples for a cytological examination are collected in (EDTA) tubes with anticoagulant, and in sterile tubes without anticoagulant for visual inspection and cultivation.
The color of the peritoneal liquid is normally clear, serous types and not coagulate. Murky peritoneal liquid may indicate an increase in white blood cells and whole protein. If it is pinkish or reddish this indicates free hemoglobin or hemorrhage and if it is dark brown or green and has a malodorous smell it can suggest intestinal rupture.

The protein content is usually less than 2.5 g/dl. Larger numbers suggest an inflammatory process or vascular occlusion with the loss of fluids and protein. Fibrinogen values that are greater than 10 mg/dl indicate acute contamination or hemocontamination. The normal cell count is 5-10,000. Increased values indicate progressive vascular damage and intra-abdominal diapedesis. Increases in white blood cells and protein without increase in red blood cells indicate peritonitis or abdominal abscesses. Acute infections produce an increase of neutrophils and fundamentally and total increase of mononuclear cells.

The presence of free or phagocytized bacterias indicate ischemia and the release of bacteria and endotoxins (not to be confused with intestinal liquid).