An obsolete term for what was once considered an intermediary product of coagulation but is no longer thought to exist. ... (05 Mar 2000) ... 
Activated Blood Factor V which acts on prothrombin to generate thrombin during blood coagulation.
Type: Term Pronunciation: ak-sel′er-in Definitions: 1. Obsolete term for what was once considered an intermediary product of coagulation but is no longer thought to exist.