THE BLOOD. 63 



mostly used) we may obtain, by saturating it with solid magnesium sul- 

 phate or sodium chloride, a white viscid substance as precipitate which 

 is called fibrinogen^ If fibrinogen be separated by filtration, it can be 

 dissolved in water, as a certain amount of the neutral salt used in pre- 

 cipitating it is entangled with the precipitate, and is sufficient to pro- 

 duce a dilute 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. The same body may also be obtained as a viscid pre- 

 cipitate from hydrocele fluid by diluting it with water, and passing a 

 brisk stream of carbon dioxide gas through the solution. 



Now if blood-serum be added to a solution of fibrinogen, obtained 

 in either of these ways, the mixture clots. 



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

 globulin very similar in properties to fibrinogen, if it be treated in 

 either of the ways by which fibrinogen is obtained from hydrocele fluid; 

 this substance is called paraglobulin, and it may be separated by filtra- 

 tion 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 respec- 

 tively 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, fibri- 

 nogen, as a flaky precipitate, by adding carefully thirteen 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 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 cor- 

 responds 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 

 associated with them in plasmine to produce coagulation; this is what 

 is known under the name of fibrin ferment (Schmidt). 



Let us now consider the evidence in favor of this view. It was at one 

 time thought that the reason why hydrocele fluid coagulated, when 

 serum was added to it, was that the latter fluid supplied the paraglobu- 

 lin which the former lacked; this, however, is not the case, as hydrocele 



