Abstract
In the pre-antibiotic era, infections were usually more frequent and serious than today. In those times, Fåhraeus reported an _in vivo_ simulation of the clinical erythrocyte sedimentation rate test that was normally carried out _in vitro_ with freshly drawn blood. This led him to propose an explanation for the finding of long white strips (“fibrin coagula”) within the blood vessels of those who had died from infections. The surge of serious infections in pandemic times has likely kindled a reemergence of the phenomenon.