THE CIRCULATING LIQUIDS OF THE BODY 35 



administration of a solution of calcium chloride has sometimes 

 been thought to lessen the tendency to haemorrhage, or its local 

 application to cut short an actual attack. It is possible that in 

 some cases there may be a want of thrombokinase in the blood 

 or in the cut tissues, and that the application of normal tissue 

 extract (extract of thymus, for example) or of a solution con- 

 taining fibrin-ferment may be of benefit. The injection of 

 normal serum into the circulation, or the transfusion of normal 

 blood, have also been used with temporary advantage. 



When sodium fluoride is added to freshly-drawn blood to the 

 amount of 0*3 per cent., coagulation is also prevented. But 

 there is this difference between oxalate and fluoride plasma 

 that, although the calcium has been precipitated in both, the 

 addition of calcium chloride to fluoride plasma is not sufficient 

 to induce clotting. Tissue extract containing thrombokinase 

 must be supplied as well. In some way or other sodium fluoride 

 interferes with the liberation of thrombokinase from the formed 

 elements of the blood, although in the concentration mentioned 

 it does not hinder the action of fully-formed thrombin, as is 

 shown by the fact that fluoride plasma coagulates on the addition 

 of a little serum, which supplies fibrin-ferment. The fluoride 

 blood clots readily if it is diluted with water, and at the same 

 time mixed with calcium chloride solution, for the water damages 

 the formed elements, and thus favours the liberation of thrombo- 

 kinase. 



When proteoses (or peptones) are injected into the circulation 

 of a dog or goose, the blood is deprived of the power of coagulation. 

 The peptone plasma must be assumed to contain both thrombogen 

 and thrombokinase, since it can be made to clot in various ways 

 (e.g., by dilution with water or by slight acidulation with acetic 

 acid) without the addition of anything which could supply either 

 of these factors. Yet a little tissue extract causes it to clot 

 much more rapidly than simple dilution or acidulation, and more 

 rapidly than the addition of serum. So that either the throm- 

 bokinase already present in peptone plasma is present in an 

 unavailable form, or in some way the formation of thrombin 

 from its precursors is hindered. But this is not the only cause 

 of the incoagulability of peptone plasma. It may be shown 

 to contain an antithrombin, a body which antagonizes the 

 action of fully-formed thrombin, and which does not seem to 

 be a ferment, since it acts quantitatively in proportion to the 

 amount present. This is the reason why, although peptone 

 plasma can always be made to clot by the addition of fibrin- 

 ferment, in serum, for instance, relatively large quantities of 

 it must be supplied (Practical Exercises, pp. 56, 57). 



An extract of the head of the medicinal leech in salt solution 



32 



