"The authors used ferritin as an electron dense tracer, such that they could visualize both the structure of the capillary wall and the pathways taken by the ferritin moelcules across the wall....This report confirmed that the basement memrane of the glomerular capillary wall efficiently retards the passage of large macromolecules, but the questions addressed in this report remain challenging more than half a century later" (Feehally et al, Landmark papers in nephrology [2013] 1.3 pp. 6-7).