Experimental studies concerning the hemorrhagic tendency due to massive blood transfusion are performed. The results obtained are summarized as follows:
1) After massive blood transfusions in rabbits the prolongation of bleeding time, clotting time, and the decrease of capillary resistance are demonstrated.
2) Platelet counts of the recipients decrease after 2-3 hours of massive transfusions and return to the normal range after 24 hours.
3) The extent of the decrease in platelet counts parallels the amount of blood transfused in the majority of cases.
4) The quantitative changes of blood coagulation factors, although definitely recognizable, do not fall much below the critical range except in a few cases.
5) The fibrinolytic phenomenon is accelerated as a rule after the transfusion.
6) The antiplasmin activity of the recipient's serum shows remarkable changes and the decrease appears to be influenced by the reduced platelet counts.