1. It has been shown that the effect on B.C.T. of anticoagulants and other substances, when used in the quantities employed in this work, is dependent on the original C.T. of the blood to which they are added.
2. The effects on blood, in vitro, of heparin and Toluidin Blue have been examined in detail; tests have also been made with Chlorazol Fast Pink, adrenalin, and histamine preparations.
3. Reason has been given for the view that heparin is not ordinarily present in the blood. A principle, which is not heparin, has been shown to exist in the blood which can result in wide variations in B.C.T.
4. The amount of anti‐heparin substances in the blood has been investigated.
5. The effects of trauma have been shown to include the presence in the blood of two substances which affect B.C.T. and which have been referred to as Discharges A and B.
6. Discharge A is produced locally and probably regionally, and is a chemically basic substance. Its effect on B.C.T. is to reduce it to 5 minutes, but not lower.
7. Discharge B is produced generally, and is of the nature of heparin. It combines with Discharge A, and its flow is intermittent.
8. The view is advanced that, if Discharge A is a shock‐producing substance, then Discharge B is the natural antidote to it.
We are indebted for assistance in this work to many people. Our thanks are offered in particular to Profs. Durward and Hemingway, of Leeds Medical School, who have been helpful in many ways; to Prof. D. Burns, in connection with whose department in Newcastle‐upon‐Tyne this work has been done, who has granted facilities there when needed, and whose advice, keen interest, and encouragement have been of much value; to the Medical Research Council and to the Beaverbrook Fund of King's College Medical School, a grant from each of which, to S.B.S., made possible the earlier stages of this work, and to the Research Fund Committee of King's College for a grant to S.B.S.; and finally to the large number of people of Ossett, Yorks, who have very kindly supplied blood.
