Blood donor lying down, with a tube inserted in his forearm to collect blood. He is squeezing a rubber ball to encourage good circulation in his arm. The collected blood is drained into a bag (centre right) that contains an anti-coagulant so the blood remains liquid. The bag is suspended on a set of scales so that the nurses (phlebotomists) can monitor the amount collected. Typically a full bag will hold 475 millilitres. Donor blood is given to patients in transfusions to replace lost blood, for example during surgery or after accidents.