“…T h e leucocyte rhythm is not affected by feeding, but unlike that of pigeons it is affected by activity (Zirm & Bauermeister, 1933). A rhythm in the number of red corpuscles has been found by Rosenbaum (1951) in man, and by Engstrom, Holmgren & Walhfart (1938) in rats in which there is also a reticulocyte rhythm affected by feeding (Goldeck & Stoffregen, 1952). Thrombocyte number and clot retraction time (the time taken for a clot of blood to retract in a firm mass from which the plasma may be separated) show a rhythm in man (Matis & Gross, 1951).…”