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1. 1. The subcellular localization of Ca2+/Mg2+-stimulated ATPase in human platelets was studied. The effect of thrombin on the enzyme was also investigated. 2. 2. Characterization of the ATPase activity in platelet lysates revealed some similarities with actomyosin ATPase in its response to divalent cations. 3. 3. Both Ca2+- and Mg2+-stimulated ATPases were found to be localized in a granular fraction containing the platelet-bound adenine nucleotides. 4. 4. Thrombin did not cause the release of Ca2+/Mg2+-activated ATPase from washed human platelets. 5. 5. A slight inhibition of Ca2+-stimulated ATPase occurred 10 sec after exposure of washed human platelets to thrombin. 6. 6. That Ca2+/Mg2+-stimulated ATPase occurs in granules containing adenine nucleotides seems established. However, although a slight drop in ATPase activity occurred after the addition of thrombin to washed platelets, no evidence of ATPase activation during the release phenomenon was obtained.

In 10 children with Politano and Leadbetter's antireflux operation, tranexamic acid reduced the blood loss, especially postoperatively. In three patients renewed bleeding occurred when the treatment stopped. Antifibrinolytic treatment probably reduced the need for blood transfusions in these operations. In six children, however, large clots were passed with the urine from the fourth to the ninth day postoperatively, probably due to inhibition of the advantageous clot lysis.

It has been demonstrated that acetylsalicylic acid, butazolidine, colchicine, hydrocortisone, chlorpromazine and imipramine inhibit the uptake of polystyrene latex particles and oxygen consumption during phagocytosis by human leucocytes.

A technique for electronic platelet counting is described. The erythrocytes in whole blood were removed by sedimentation at 1 × g in a two-phase system, using dextran as the erythrocyte-aggregating agent. The platelets in the plasma layer were counted electronically. By means of the haematocrit value, the plasma platelet count was converted to whole blood platelet count, which corresponded well with the microscope count. At low platelet numbers, corrections must be made for contaminating erythrocytes and leucocytes. At low platelet numbers, both microscope counts and celloscope counts became inaccurate. For the use of electronic counting in clinical medicine, this difficulty can easily be avoided by reducing the degree of dilution.

SUMMARY The relation between milk ejection and antidiuretic response was studied on lactating cows using different stimuli. The stimuli, utilized to induce milk ejection, could be classified according to increasing effectiveness as follows: (1) showing the calf to the mother (visual stimulation); (2) washing the udder with water at 40° C in trained animals; (3) washing combined with visual stimulation; (4) suckling. Experimental conditions (hydration, bladder catheter) exerted a marked inhibiting effect in most animals on the milk-ejecting reflex induced by stimuli 1, 2 and 3. The reactions of domesticated cows under these circumstances are analogous to those of primitive breeds under normal conditions. Generally, the antidiuretic response seemed to be quantitatively correlated with the release of oxytocin. However, exceptions to this rule were observed. An antidiuretic response was obtained in cows after milk ejection unaccompanied by withdrawal of milk. The effect of known amounts of oxytocin on milk ejection was studied, and the dose-response curve was nearly a straight line when log dose was plotted against the volume of milk ejected. The slope of the curves, however, varied in different cows.

A survey is given of the most recent work on interrelations between the coagulation and kinin systems. The recent identification of the Fletcher factor with prekallikrein has established another link between the clotting and kinin systems besides factor XII. Further links are provided by the cold activation of factor VII by factor XII-prekallikrein, and the feedback activation of factor XII by kallikrein. These new apprehensions also have consequences for the theory of intrinsic clotting, and the relation between the intrinsic and extrinsic system, and emphasize the complex function of factor XII.

Summary and Conclusions1. Moderate doses of heparin often prolonged the bleeding time in men, rats and mice. The bleeding was wavelike, and a sensitive method was necessary to demonstrate the prolongation.2. Large doses gave a prolonged bleeding time, and the bleeding was often profuse and continuous.3. Heparin did not produce thrombocytopenia. Moderate doses probably prevent viscous metamorphosis and fibrin formation, resulting in large but inefficient platelet plugs. Large doses may also interfere with the aggregation of platelets, preventing the formation of platelet plugs.

Plasma factor 7 was found increased to 5-20 times normal in the plasma stored overnight between -5 and 0 degrees C in women using oral contraceptives. This might cause the observed shortening of thrombotest time in stored plasma. The activation of factor 7 is dependent on facto r 12. The system was inhibited by trasylol and soybean trypsin inhibitor (STI). Epsilon aminocaproic acid (EACA) or aminomethyl cyclohexane-carboxylic acid (AMCA) had no effect.

The relationship between oral contraceptive (OC) use and thrombosis is discussed. OC use causes change sin coagulation, fibrinolytic, and blood vessel mechanisms, but these changes in themselves may not cause significantly higher frequency of thrombosis. OC use does lead to an increased incidence of thrombosis, which is ascribed to the estrogen component. The incidence of thrombosis with OC use is about 1/3 of that occurring naturally during pregnancy and puerperium. Care should be taken to prevent women with predisposition to thrombosis from using oral contraceptives.

Patients with increased haemolysis following insertion of heart valve prostheses showed a significantly increased platelet consumption and a marked decrease of adhesive platelets. Possibly, adhesive platelets are consumed by formation of platelet thrombi on the artificial valves. The high prevalence of thrombo-embolism in patients with ball valves might be explained by such a mechanism.