the difference between the transmittance of the prp and that of the plasma containing no platelets to determine the aggregation property a blood sample as prepared in the same manner as described above was analyzed to determine the adhesiveness of platelets in accordance with a modification of the method of a j hellem et al scand j haemat 7 374 1970 that is 1 ml of the blood sample was allowed to fall due to by gravity through a vinyl tubular column having an inside diameter of 3 mm and a length of 13 cm packed with glass beads the difference between the number of platelets in the blood sample prior to passing through the column and that in the blood sample after passing through the column was divided by the number of platelets in the blood sample prior to passing through the column and the value obtained was taken as the adhesiveness of platelets in this case opc or a physiological salt solution was previously added to the blood in an amount of 1 10 volume of the blood and the resulting sample was incubated for 10 minutes before passing through the column the procedure for the determination used in each case will be described in greater detail in the examples hereinafter given the effect of opc on adp induced platelet aggregation was evaluated as follows blood was drawn from a healthy male adult human into a syringe previously containing 3 8 sodium citrate in a volume.