THE COAGULATION OF THE BLOOD 217 



A pure solution of fibrinogen may be kept at ordinary temperatures for an 

 indefinte period of time without its yielding even traces of fibrin. A perfectly 

 typical coagulum, however, may be produced, if either a washed fibrin-clot, a small 

 quantity of blood serum, or a solution containing thrombin is added to it. 



Fibrinogen is a protein. It belongs to the group of the globulins. From para- 

 globulin, it may be distinguished in several ways ; viz. : it coagulates at a lower tem- 

 perature (55° to 60°), is completely precipitated by saturation with sodium chlorid 

 or magnesium sulphate, and may be converted into the insoluble protein, fibrin. 

 Its percentage composition has been given by Hammarsten as: C 52.93, H 6.90, 

 N 16.66, S 1.25, O 22.26. According to Schmiedeberg its molecular composition 



is: Cl08Hi62N3oS034. 



Fibrin. — In accordance with the analyses of Hammarsten, fibrin possesses the 

 same composition as fibrinogen. This similarity, however, is only an apparent 

 one, because as both substances are extracted with alcohol and ether, the fat and 

 lipoid are not included inj the analysis, and hence, the remaining substance 

 appears as a protein of the composition just given. Wooldridge, ^ in fact, believes 

 that these bodies are not identical at all but show certain differences in the lipin 

 part of their molecules. Fibrinogen as it exists in the plasma is regarded as a 

 iecithoprotein or as a substance containing much phospholipin. Fibrin is similarly 

 constituted, but contains less phospholipin. The chemical process underlying the 

 formation of the relatively insoluble fibrin is not clearly understood. Fibrinogen 

 is said to change first into soluble fibrin, and later on into fibrin proper. In accord- 

 ance with Hammarsten, 2 a hydrolysis results which splits the molecule of the fibrin- 

 ogen into fibrin and fibrinoglobulin. Other investigators, however, assume that 

 physicochemical alterations are incited which lead to an intramolecular rearrange- 

 ment of the fibrinogen. Thus, fibrinogen is regarded as the hydrosol, and fibrin as 

 the hydrogel of one and the same globulin. ^ It is also supposed that a precipita- 

 tion of the fibrinogen by electrolytes takes place soon after the thrombin has incited 

 its decomposition.* 



If the blood is beaten with a rough piece of wood while it is being withdrawn 

 from the blood-vessel, the fibrin accumulates upon the stick in the form of an 

 elastic fibrous mass, the springiness of which is lessened as soon as the shreds are 

 torn or are separated from their attachments. This deposit is always contamin- 

 ated with red corpuscles and lymphoid cells. If it is essential to obtain this sub- 

 stance in a pure form, it should be prepared from filtered plasma, or from filtered 

 transudates; moreover, it should be noted that if it is allowed to remain in contact 

 with the blood from which it has been removed, it dissolves in part. While the 

 factors which are responsible for this fibrinolysis are not known, it is believed that 

 they are of enzymic origin. Fibrin derived from the blood of different animals, 

 exhibits somewhat different properties. It is insoluble in water, alcohol and ether, 

 but may be dissolved in dilute salt solutions at a temperature of 40° C. 



B. INTRAVASCULAR CLOTTING 



It has been found that the blood retains its fluid condition only as 

 long as it is permitted to remain in contact with the normal intima of 

 the blood-vessels. This statement implies that coagulation must set 

 in as soon as the blood is brought in relation with a foreign body, 

 whether this be outside or inside the vascular channels. Intravascular 



1 Collected papers, Rep. to the Scient. Comm. of the Grocer's Assoc, i, 201; 

 ii, 266. 



2 This view is also held by Schmiedeberg (Archiv fiir Exp. Path, und Pharm., 

 xxxix) and Heubner (ibid., xlix, 1903, 229). ' 



2 Iscovesco, Soc. Biol., Ix andlxi, 1906. 



* Friedemann and Friedenthal, Zeitschr. fiir exp. Path., iii, 1906, 73. 



