These materials are used to control bleeding when it cannot be checked by more conventional means. They are gradually absorbed by the tissues; therefore, if used during surgery, they can be left in the body when the incision is closed, and if applied to a surface wound, they need not be removed when the dressing is changed. There are four important types of absorbable hemostats, namely human fibrin foam, gelatin sponge, oxidized cellulose and calcium alginate. Fibrin foam is the most acceptable one because it is of human origin and is particularly well tolerated by the tissues, but its supplies are limited.