In the pre-antibiotic era, infections were usually more frequent and serious than today. Robin Fåhraeus examined the erythrocyte sedimentation rate (ESR) test, which was normally carried out _in vitro _with freshly drawn blood. His extensive studies on the mechanism and physiological significance of the enhanced sedimentation of erythrocyte aggregates in disease included its _in vivo _simulation. 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. His speculations that the importance of the serum-dependent red blood cell (RBC) aggregation phenomenon extends beyond the clinic, has led to immunologically significant entropic interpretations of infection-associated aggregations, both cellular (e.g., RBCs) and macromolecular (i.e., polymerizations).