Light micrograph of the lines of Zahn in a thrombus (blood clot). The lines are formed of alternating layers of red blood cells (darker red) and fibrin (light pink). The presence of the lines of Zahn indicate that the blood clot has formed before death. This fact is useful for a pathologist performing an autopsy, as the pathologist may need to evaluate whether a clot formed before or after death, the latter of which would not have contributed to the patient??? demise. Haematoxylin and eosin stained tissue section. Magnification: 40x when printed at 10 cm.