THE COAGULATION OF THE BLOOD 949 



two forms of plasma we can arrive at a conception of the processes of 

 coagulation which enables us to understand the behaviour of all these 

 various types. We may take as our type oxalate plasma. Oxalate 

 plasma, as procured by centrifuging a specimen of horse's blood con- 

 taining 01 per cent, sodium oxalate, is a clear yellow fluid, perfectly 

 free from formed elements, which evinces no tendency to clot. On 

 adding a drop of calcium chloride to such plasma we see that it contains 

 an excess of oxalate from the production of a precipitate of calcium 

 oxalate. If calcium chloride be added drop by drop so as to be present 

 in slight excess and the plasma be then kept warm, it will clot within 

 a time varying from a few minutes to an hour. The clot thus formed 

 is perfectly firm and the vessel can be inverted without any of its 

 contents flowing out. Very often no retraction of the clot takes place, 

 but if it be pressed with a glass rod or with the fingers a clear serum 

 is squeezed out and a mass of pure fibrin remains. The place of lime 

 can be taken by strontium, but barium and magnesium are powerless 

 to initiate clotting. We must therefore conclude that the presence 

 of a soluble calcium salt is one factor of those necessary for coagulation. 

 This is borne out by the fact that a similar uncoagulable blood is 

 produced by the action of sodium fluoride. Some difficulty, however, 

 was felt when it was found that sodium citrate might be used instead 

 of sodium oxalate or chloride, since sodium citrate does not produce 

 in the blood any precipitate of insoluble lime salts. Here therefore 

 we have a blood containing lime in solution and yet uncoagulable. 

 The difficulty has been cleared up by the work of Sabbatani and 

 C. J. Martin. When sodium citrate is added to a lime salt a double 

 salt of sodium calcium citrate is formed in which the calcium is in the 

 anion and forms part of the acidic radical. The mere presence of 

 dissolved calcium is not sufficient for clotting to take place. It is 

 necessary that the calcium should be in the form of a salt and in an 

 ionised condition, such as calcium chloride or calcium sulphate. 



Though calcium is a necessary condition for the occurrence of 

 coagulation, it cannot be regarded as a precursor of the protein fibrin. 

 If the composition of the plasma before coagulation has been set up 

 be compared with that of the serum which has separated from the 

 clot, it is found that plasma contains a protein, fibrinogen, not repre- 

 sented in the serum, which must therefore be the precursor of fibrin- 

 Fibrinogen belongs to the class of globulins. It can be separated from 

 oxalate plasma by half -saturation with common salt. An equal 

 volume of a saturated solution of sodium chloride is added to plasma 

 so that the whole mixture contains 16 per cent, sodium chloride. The 

 fluid gradually becomes turbid from the production of a precipitate 

 which, at first granular, rapidly aggregates to form a stringy, 

 slimy solid, and on stirring aggregates into masses which adhere 



