Abstract: A cradle for use in blood donating processes comprises surface (2) which is intended to support a blood-collecting bag and to be rocked reciprocatingly on an axle (4) which extends perpendicularly to the surface, by means of a crank (5, 7). The cradle is provided with a weight measuring device (8) which functions to measure the quantity of blood that has flowed into the bag, and is also fitted with a clamping device (11) which functions to clamp-on or squeeze the hose such as to prevent blood from flowing therein and which is operable electromagnetically. The cradle is further provided with a control circuit (21) which is constructed to control at least the clamping device (11).