This substance is layered over Ficoll–Paque (“FYE-cull-pack”) in a protocol for isolating PBMCs that employs a density gradient. This substance is treated with EDTA or heparin to stabilize it for analysis. During World War II, Edwin J. Cohn devised a purification protocol for extracting albumin from this (10[1])substance. A thin layer of this substance is spread on a glass slide and examined under a microscope in a “peripheral smear.” This substance is centrifuged to fractionate it into two layers separated by a buffy coat and can be analyzed to calculate hematocrit. For 10 points, a fingerprick can be used to extract what substance composed of leukocytes, erythrocytes, and plasma? ■END■