166 THE BLOOD. 



substance which possesses the property of converting fibrinogen into 

 fibrin, and is, according to Pekelharing, a combination of the nucleo- 

 proteid with lime, and identical with the fibrin ferment of A. Schmidt. 

 The fibrin ferment is sometimes spoken of as "thrombin," and the 

 nucleo-proteid material in the plasma from which it is produced is then 

 termed " prothrombin." 



Wooldridge 1 found that, on subjecting peptone plasma to cold, he 

 obtained a finely granular deposit, which had the property of producing 

 clotting in fibrinogenous fluids, which are not themselves spontaneously 

 coagulable, and of accelerating the process of clotting in coagulable fluids. 

 To the material thus obtained, and which he described as having, under 

 the microscope, an appearance similar to masses of blood platelets, he 

 gave the name " A-fibrinogen," because *he found that on adding it to 

 peptone plasma it produced fibrin, and that the amount of coagulation 

 was more or less proportional to the amount of A-fibrinogen added. It 

 is not fibrinogen as the term is ordinarily used, but is probably either a 

 micleo-proteid, or a mixture of nucleo-proteid with globulin. A similar 

 deposit occurs, as already stated, in oxalate plasma, on standing in the 

 cold. A precipitate containing the same substance is also produced by 

 adding magnesium sulphate solution in considerable amount to blood, and 

 in both plasma and serum of certain animals on acidulation with acetic 

 acid, but in both cases it is liable to be mixed with serum globulin. 

 It also occasionally occurs in serum, on standing, even without the 

 application of cold. Halliburton has suggested that the deposit in 

 peptone plasma may be a part of the proteoses, which were injected into 

 the blood, for he found that solutions of albumose were liable to give a 

 similar deposit on cooling by means of ice, but there is not enough proteose 

 present in peptone plasma to account for such deposit, and the fact that it 

 occurs under other conditions in plasma also negatives this supposition. 

 These experiments of Wooldridge, and the behaviour of the body termed 

 by him A-fibrinogen, will be again referred to in a subsequent section. 



Fibrin. Fibrin is the chief substance formed from fibrinogen in the 

 coagulation of blood plasma, and it is also produced in the coagulation of 

 lymph and other fibrinogen-containing fluids. It is usually got by whipping 

 blood as it flows from the blood vessels with a bundle of wires or glass 

 rods before it has had time to coagulate into a solid mass. The coagulum 

 then forms upon the wires or rods, and can be washed free from adherent 

 red corpuscles by putting it under a stream of water for a few hours. 

 But to obtain pure fibrin it is necessary first to prepare fibrinogen from 

 blood plasma by precipitation with NaCl (half -saturated), to purify this 

 by re-solution and re-precipitation, and finally to cause the coagulation of 

 the fibrinogen solution by fibrin ferment. The clot thus obtained, which 

 must be thoroughly washed, is composed of nearly pure fibrin. 



When obtained by whipping blood, fibrin is a white stringy substance 

 when wet, drying to a glue-like mass. The threads of which it is com- 

 posed, and which, as may be seen in a microscopic preparation of blood, 

 interlace with one another and form a network of the finest possible 

 filaments, entangling the blood corpuscles in its meshes, have a strong 

 tendency to retract or shorten when formed ; this is the reason why a 

 clot shrinks and expresses serum from its interior. Fibrin is slowly 

 soluble in 5 to 10 per cent, solutions of certain salts, such as sodium 

 chloride, sodium sulphate, potassium nitrate, magnesium sulphate, and 



1 Wright, Lancet, London, 1892, vol. i. pp. 457, 535. 



