. 



16 COAGULATION OF BLOOD. [BOOK i. 



Uts influence lessened by dilution. With the removal of the 

 (substance precipitated, the plasma has lost its power of coagu- 

 lating. 



If the precipitate itself, after being washed with a saturated 

 solution of the neutral salt (in which it is insoluble) so as to get 

 rid of all serum and other constituents of the plasma, be treated 

 with a small quantity of water, it readily dissolves 1 , and the solution 

 rapidly filtered gives a clear colourless filtrate, which is at first 

 rfectly fluid. Soon however the fluidity gives way to viscidity, 

 and this in turn to a jelly condition, and finally the jelly shrinks 

 into a clot floating in a clear fluid; in other words, the filtrate 

 clots like plasma. Thus there is present in cooled plasma, and 

 in plasma kept from clotting by the presence of neutral salts, 

 a something, precipitable by saturation with neutral salts, a some- 

 thing which, since it is soluble in very dilute saline solutions, 

 cannot be fibrin itself, but which in solution speedily gives rise to 

 the appearance of fibrin. To this substance its discoverer, Denis, 

 gave the name of plasmine. We are justified in saying that the 

 coagulation of blood is the result of the conversion of plasmine 

 I or some part of plasmine into fibrin. 



But there are reasons for thinking that plasmine is a mixture 

 of at least two bodies. If sodium chloride be carefully added to 

 plasma to an extent of about 13 per cent, a white flaky viscid 

 precipitate is thrown down very much like plasmine. If after 

 the removal of the first precipitate more sodium chloride, and 

 especially if magnesium sulphate, be added a second precipitate 

 is thrown down, less viscid and more granular than the first. 

 The name fibrinogen is given to the former, paraglobulin to the 

 latter. Both are proteids belonging to the globulin family 2 , the 

 members of which while insoluble in distilled water are readily 

 soluble in dilute solutions of neutral salts. According to some 

 authors solutions of fibrinogen are characterized by their being 

 precipitated, and coagulated 3 at a temperature of about 55 60 

 while solutions of paraglobulin are not so changed till the tempe- 

 rature rises to 68 70. There are also other differences (see 

 Appendix). 



Both these substances are thrown down when plasma is 

 saturated with sodium chloride so that the plasmine of Denis 

 appears to be a mixture of fibrinogen and paraglobulin, and the 

 question arises, Are both these concerned in the formation of fibrin ? 



Paraglobulin J hoi only occurs as a constituent of plasma, but 

 is found in considerable quantity in the serum left after clotting ; 

 it forms as we shall see a large portion of the proteids present in 



1 The substance itself is not soluble in distilled water, but a quantity of the 

 neutral salts always clings to the precipitate, and thus the addition of water virtually 

 gives rise to a dilute saline solution, in which the substance is readily soluble. 



2 See Appendix. 



3 See Appendix for the distinction between the coagulation of proteids by heat, 

 and the coagulation due to the appearance of fibrin. 



