Summary
1 During clotting, pigs’ plasma developed thromboplastic activity. This activity was
compared with that of thrombin in accelerating the clotting of platelet-deficient
plasma and of fibrinogen in the presence and absence of calcium.
2. The thromboplastic activity of the plasma could be mimicked by a solution of thrombin
of the right strength.
3. The thromboplastic activity could be stabilised by freezing but disappeared rapidly
at 37° C. Thrombin added to the serum was inactivated at almost exactly the same rate;
and the rates of loss of both activities were considerably reduced by cooling, by
decalcification with sodium ethylene-diaminetetraacetate, and by acidification.
4. It is concluded that the thromboplastic activity of undiluted recalcified pigs’
plasma can be accounted for by its thrombin content alone. It also seems likely that
the activity measured in the screening test for disorders of thromboplastin generation
described by Hicks and Pitney (1957) can be attributed wholly to thrombin.
