At this stage of cellular hemostasis the released ADP induces the aggregation of thrombocytes as the “white” thrombus grows. This process is at first reversible. The aggregates can still let the plasma in, and thrombocytes are preserved both structurally and functionally. Reversible aggregation can change into irreversible one. During this thrombocytes undergo alterations that are microscopically visible. With the help of electronic microscopy, it has been determined that the morphological alterations occur in the following order: preagglutination, agglutination, thrombocytorhexis, and thrombocytolysis.