266 THE BLOOD. 



lation of the blood do not occur normally in the bloodvessels during life, 

 the most important facts bearing on this point are that the blood of the 

 renal and hepatic veins yields no fibrine, or much less than arterial blood. 

 The substance which causes coagulation, therefore, is decomposed and 

 disappears from the blood while passing through the liver and the kidneys. 

 This is established by the observations of Simon, Lehmann, and Brown- 

 Sequard. While an abundance of fibrine may be obtained from either 

 arterial or portal blood, none or only feeble traces of it are to be found 

 in that of the hepatic or the renal veins. This substance, being con- 

 stantly eliminated from the blood in this way by the liver and kidneys, is 

 necessarily produced afresh elsewhere at the same time, since its quan- 

 tity in the blood remains unchanged ; and the new material thus formed 

 is also rapidly altered by a continuation of the same process. -By 

 calculating approximately the quantity of blood contained in the whole 

 body and that passing daily through the liver and kidneys, it appears 

 that a quantity of fibrine equal to that in the entire blood must be de- 

 stroyed and reproduced several times over in the course of a single day. 

 Thus the fibrine which appears in a specimen of blood drawn from the 

 vessels at any one time, and which causes its coagulation, is derived 

 from a substance of very recent formation ; and, if allowed to remain in 

 the bloodvessels, it would have disappeared by metamorphosis before 

 arriving at the stage of coagulation. 



Usefulness of Fibrine and of its property of Coagulation. Although 

 the fibrine of the blood, from its small quantity and the general charac- t 

 ter of its properties, does not seem to take a direct part in the more 

 essential phenomena of nutrition, it is still a very important ingredient 

 of the circulating fluid. Upon the presence of this substance depends 

 the process by which nature effects the arrest of hemorrhage from 

 divided or ruptured bloodvessels. Whenever a wound is accidentally 

 made in vascular tissues, the blood at first flows freely from the external 

 orifice. But a portion of the blood coagulates upon the edges of the 

 wound, and after a time the successive deposits of cogulated fibrine 

 become sufficient to effectually close the opening and prevent further 

 loss of blood. The proper treatment for wounds of moderate size, in 

 which only the veins and capillaries, or small arteries, have been divided, 

 is simply to apply compression and to keep the edges of the wound in 

 contact continuously for fifteen or twenty minutes. By this time the 

 thin layer of blood between the wounded surfaces, thus kept at rest, has 

 coagulated, and the hemorrhage does not reappear when the artificial 

 compression is removed. If a larger artery be opened, the force with 

 which the blood is expelled prevents local coagulation, or is sufficient 

 to detach the coagula after they are formed. In such cases accordingly 

 the surgeon places a ligature upon the wounded artery itself, and in this 

 way effectually controls the hemorrhage. But even in this instance the 

 ligature is only a means of applying compression for a longer time, and 

 is still temporary, as it must come away again when it ulcerates through 

 the coats of the vessel. The immediate and essential means of stopping 



