SummaryThe anti-heparin activity of the thrombocytes can be attributed to that part of the thrombocytes that is unsoluble in Bloor solution, viz. factor 3. This activity is directly proportional to the concentration. Factor 3 is thermostable and inhibits the formation of thromboplastin.Factor 4, the thromboplastic component, can be extracted from the thrombocytes with the aid of Bloor mixture. This activity is thermolabile, but remains present during storage at—20°C; it can be absorbed by barium sulphate.