84G PHYSIOLOGY 



therefore conclude that mere contact with a foreign body has a direct 

 destructive action either on the plasma leading to the formation of blood- 

 platelets, or on the latter, leading to their disintegration and the discharge 

 of thrombokinase. Birds' blood, for instance, can be made to clot without 

 the addition of tissue juice if, by increasing the mechanical insult, as by 

 violent whipping, filtration through a clay cell, or addition of water, we 

 destroy the leucocytes and red blood-corpuscles, so leading to the liberation 

 of their contained thrombokinase. Another factor is probably the presence 

 of what we may call antithrombins in circulating blood. Although evidence 

 of the existence of these bodies is still somewhat uncertain, the fact that 

 blood-serum often has an inhibitory effect on the action of a solution of fibrin 

 ferment points to the presence in the serum of some antibody to the ferment. 

 One must assume too that processes of disintegration are continually oc- 

 curring in the blood and involving the plasma, blood- platelets, and leucocytes, 

 just as we know them to affect the red blood- corpuscles. In the healthy 

 animal the liberation of thrombokinase which must take place under these 

 circumstances has no influence in producing clotting. The organism therefore 

 must possess means of neutralising the presence of small quantities either of 

 kinase or of fibrin ferment. When small quantities of either of these sub- 

 stances are injected into the blood-stream no coagulation takes place, but the 

 blood obtained after the injection clots with less readiness than before, a 

 change which can only be ascribed to the production in the body of anti- 

 kinase or of antithrombin. This production of anticoagulins must be 

 continually taking place and must co-operate in the preservation of the fluid 

 state of the blood while in the vessels. 



INTRAVASCULAR CLOTTING. On account of the protective mechan- 

 isms with which the animal organism is endowed the production of clotting 

 in the vessels of the living animal is not readily effected by the injection 

 of thrombin. Solutions obtained by Schmidt's method from alcohol- 

 coagulated serum are generally without effect, and we have to inject a 

 very strong solution of thrombin or the strong fibrin ferment contained in the 

 venom of certain snakes in order to bring about coagulation of the blood in 

 the vessels. Intra vascular clotting is more easily effected by the injection of 

 thrombokinase. It was shown by Wooldridge that normal saline extracts 

 of tissues rich in cells, such as the thymus, lymph-glands, or testis, causes 

 invariably extensive thrombosis. If such extracts be acidified with acetic 

 acid a precipitate is produced which is soluble in dilute alkalies, and on 

 gastric digestion yields a precipitate rich in phosphorus. Alkaline solutions 

 of the acid precipitate bring about intra vascular clotting when injected into 

 the blood- stream. According to Wooldridge the injected substance takes 

 part in the formation of the clot, and he therefore gave it the name of ' tissue 

 fibrinogen.' It is usual to regard these tissue fibrinogens as nucleo-proteins. 

 They are certainly rich in lecithin, and the precipitate obtained from them'on 

 gastric digestion may contain as much as 25 per cent, of this substance. 

 They must be derived either from the cytoplasm or from the interstitial 

 fluid of the tissues, and it is still doubtful whether we are justified in giving 



