A n n Arbor, Michigan 146 CRC Critical Reviews in Clinical Laboratory Sciences *Paracoagulability is defined as the ability to gel plasma by means other than those which cause thegenerationof thrombin. October 1977 149 FIGURE 5. Electron micrograph of fibrin strands in a vessel lumen. Arrows correspond to electron-dense bands of approximately 220 A periodicity. The sample was fixed in glutaraldehyde and osmic acid and stained with uranyl acetate and lead citrate. Magnification X 93,365. (Courtesy of Dr.