The Interaction of Living Red Blood Cells

Shed human blood clots in a minute or so; that is the fluid turns into a jelly. If a clot is examined by microscope the red cells (erythrocytes), which outnumber the white cells a thousand times, are not oriented at random but display a pseudostructure. Red cells are biconcave discs 8 micrometres in diameter and the thickness of the rounded rim of the disc is about 2 micrometres. There is some spread in these dimensions in a single sample of blood. The pseudostructure comprises a stacking of the discs face to face, superimposed on a random packing of the stacks. This so-called rouleau-formation has been observed and studied for over a century (Fahraeus 1929; Rowlands and Skibo 1972).