CHAP, i.] BLOOD. 23 



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, precipi table 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. 



The substance thus precipitated is not however a single body 

 but 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 second precipitate when examined is found to be identical 

 with the paraglobulin, coagulating at 75 C., which we have 

 already seen to be a constituent of serum. 



The first precipitate is also a proteid belonging to the globulin 

 group, but differs from paraglobulin not only in being more 

 readily precipitated by sodium chloride, and in being when 

 precipitated more viscid, but also in other respects, and especially 

 in being coagulated at a far lower temperature than paraglobulin, 

 viz. at 56 C. Now, while isolated paraglobulin cannot by any 

 means known to us be converted into fibrin, and its presence in 

 the so-called plasmine does not seem to be essential to the for- 

 mation of fibrin out of plasmine, the presence in plasmine of the 

 body coagulating at 56 C. does seem essential to the conversion 

 of plasmine into fibrin ; and we have reason for thinking that it is 

 itself converted, in part at least, into fibrin. Hence it has received 

 the name of fibrinogen. 



20. The reasons for this view are as follows. 



Besides blood, which clots naturally when shed, there are 

 certain fluids in the body which do not clot naturally, either in 

 the body or when shed, but which by certain artificial means may 

 be made to clot, and in clotting to yield quite normal fibrin. 

 Thus the so-called serous fluid taken some hours after death 1 

 from the pericardial, pleural, or peritoneal cavities, the fluid found in 

 the enlarged serous sac of the testis, known as hydrocele fluid, and 

 other similar fluids, will in the majority of cases, when obtained free 

 from blood or other admixtures, remain fluid almost indefinitely, 

 shewing no disposition whatever to clot. 2 Yet in most cases at 



1 If it be removed immediately after death it generally clots readily and firmly, 

 giving a colourless clot consisting of fibrin and white corpuscles. 



2 In some specimens, however, a spontaneous coagulation, generally slight, but in 

 exceptional cases massive, may be observed. 



