THE BLOOD. 135 



tendency of itself to coagulate. The clot produced consists of fibrin, 

 and the clotting is identical with the clotting of plasma. From the 

 serous fluid (that from the inflamed tunica vaginalis testis or hydrocele 

 fluid is mostly used) we may obtain, by half-saturating it with solid 

 sodium chloride, a white viscid substance as a precipitate which is 

 called fibrinogen. If fibrinogen be separated by filtration, it can be dis- 

 solved in water, as a certain amount of the neutral salt used in precipi- 

 tating it is entangled with the precipitate, and is sufficient to produce a 

 dilute (6 to 8 per cent) saline solution in which fibrinogen, being a body 

 of the globulin class, is soluble. The solution of fibrinogen has no 

 tendency to clot of itself, but if blood-serum be added to a solution of 

 fibrinogen, the mixture clots. 



On the other hand from blood-serum may be obtained, by saturation 

 with one of the neutral salts above-mentioned, a globulin very similar 

 in properties to fibrinogen, which is called serumglobulin or paraglobu- 

 lin, and it may be separated by filtration and dissolved in a dilute saline 

 solution in a manner similar to fibrinogen. 



If the solutions of fibrinogen and paraglobulin be mixed, the mix- 

 ture cannot be distinguished from a solution of plasmine, and in a great 

 majority of cases firmly clots like that solution, whereas a mixture of 

 the hydrocele fluid and serum, from which these bodies have been re- 

 spectively taken, no longer manifests the like property. 



In addition to this evidence of the compound nature of plasmine, it 

 may be further shown that, if sufficient care be taken, both fibrinogen 

 and paraglobulin may be separately obtained from plasma: the one, 

 fibrinogen, as a flaky precipitate by adding carefully 13 per cent of 

 crystalline sodium chloride to it; and the other, paraglobulin, may be 

 precipitated, after the removal of fibrinogen by filtration, on the further 

 addition (above 20 per cent and to saturation) of the same salt or of 

 magnesium sulphate to the filtrate. It is evident, therefore, that both 

 these substances must be thrown down together when plasma is at once 

 saturated with sodium chloride or magnesium sulphate, and that the 

 mixture of the two corresponds with plasmine. 



So far it has been shown that plasmine, the antecedent of fibrin, to 

 the possession of which blood owes its power of coagulating, is not a 

 simple body, but is composed of at least two factors viz., fibrinogen 

 and paraglobulin; there is reason for believing that yet another body 

 is precipitated with them in plasmine. 



It was at one time thought that the reason why hydrocele fluid 

 coagulated, when serum was added to it, was that the latter fluid sup- 

 plied the paraglobulin which the former lacked; this, however, is not 

 the case, as hydrocele fluid does not lack this body, and moreover, if 

 paraglobulin, obtained from diluted serum by passing a stream of car- 

 bonic acid gas through it, be added, no clotting will take place. But if 



