Blood platelets and blood clotting

That the formed elements of the blood play a part in normal coagulation has long been known. Both leucocytes and platelets have been said to yield substances which contribute to fibrin formation. Leucocytes alone, however, will not coagulate fibrinogen. Cramer and Pringle have recently shown that oxalate plasma freed from platelets by filtering through clay filters does not clot on adding an amount of CaCl2 which causes a similar centrifuged but unfiltered plasma to clot in a short time. That platelets disintegrate during coagulation, and that the addition of oxalate preserved them is well known. As early as 1881 Fano appreciated the fact that centrifuging was not sufficient to remove all cellular elements, and therefore resorted to filtration through a clay filter. Regarding the effect of other anticoagulants, it has been observed by Buerker and by Deetjen that the breaking down of platelets in shed blood as observed under the microscope was inhibited by all those substances which can be used in preventing coagulation. They mention oxalates, citrates, NaPO, Na2HPO43, salts of Mn, Fe and Ni, MgSO4, Na2CO3, peroxides and hirudin. The fact that these substances all have platelet preservative properties, does not necessarily mean that their anticoagulant effect is due solely to the fact that platelets remain intact. The experiments of Cramer and Pringle seem to show that oxalate is an anticoagulant because it preserves platelets. That this is more generally the mode of action of anticoagulants is shown by the following data. Citrate plasma gives exactly the same results as oxalate plasma, which has also been verified by others. Of greater interest than citrate are the anticoagulants which do not affect calcium.