CHAP. 1.1 BLOOD. 15 



coagulate is stirred or whipped with a bundle of rods (or anything 

 presenting a large amount of rough surface), no jelly-like coagu- 

 lation takes place, but the rods become covered with a mass of 

 shrunken fibrin. Blood thus whipped until fibrin ceases to bef 

 deposited, is found to have entirely lost its power of coagulation. 



Putting all these facts together, it is very clear that the 

 phenomena of the coagulation of blood are caused by the appear- 

 ance in the plasma of fine fibrils of fibrin. As long as these are 

 scanty, the blood is simply viscid. When they become sufficiently 

 numerous, they give the blood the firmness of a jelly. Soon after 

 their formation they begin to shrink ; and in their shrinking en- 

 close in their meshes the corpuscles, but squeeze out the fluid 

 parts of the blood. Hence the appearance of the shrunken 

 coloured clot and the colourless serum. 



Fibrin, whether obtained by whipping freshly-shed blood, or 

 by washing either a normal clot, or a clot obtained from colourless 

 plasma, exhibits the same general characters. It belongs to that 

 class of complex unstable nitrogenous bodies called proteids which 

 form a large portion of all living bodies and an essential part of 

 all protoplasm 1 . It gives the ordinary proteid reactions. It is 

 insoluble in water and in dilute saline solutions; and though it 

 swells up in dilute hydrochloric acid, it is not thereby appreciably 

 dissolved 2 . 



Coagulation then is brought about by the appearance in the; 

 blood-plasma of a substance, fibrin, which previously did not exist 

 there as such. Such a substance must have antecedents, or anj 

 antecedent what are they, or what is it ? 



If blood be received direct from the blood-vessels into one- 

 third its bulk of a saturated solution of some neutral salt such as 

 magnesium sulphate, and the two gently but thoroughly mixed, 

 coagulation, especially at a moderately low temperature, will be 

 deferred for a very long time. If the mixture be allowed to stand, 

 the corpuscles will sink, and a colourless plasma will be obtained 

 similar to the plasma gained from horse's blood by cold, except 

 that it contains an excess of the neutral salt. The presence of 

 the neutral salt has acted in the same direction as cold : it has 

 prevented the occurrence of coagulation. It has not destroyed the 

 fibrin; for if some of the plasma be diluted with from five to 

 ten times its bulk of water, it will coagulate speedily in quite a 

 normal fashion, with the production of quite normal fibrin. 



If some of the colourless transparent plasma, obtained either 

 by the action of neutral salts from any blood, or by the help of cold 

 from horse's blood, be treated with some solid neutral salt, such as 

 sodium chloride, to saturation, a white flaky somewhat sticky 

 precipitate will make its appearance. If this precipitate be re- 

 moved, the fluid is no longer coagulable. (or very slightly so), 

 even though the neutral salt present be removed by dialysis, or 



1 See Appendix. 2 For further details see Appendix. 



