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THE BLOOD. 



lated fibrine, being efficient rather by its presence, after the 

 of the ferments. 



But there is reason to believe that the fibrine-ferment, in inducing 

 coagulation, acts only on the fibrinogen, and that paraglobuline takes 

 no part in the process. According to Fredericq* the quantity of fibrine 

 obtainable from a solution of fibrinogen of known strength, is never 

 greater than that of the fibrinogen itself, coagulated by heat. This 

 would indicate that the fibrinogen alone supplies the material of the 

 coagulated fibrine, by a molecular change in its own substance, like the 

 caseine of milk when coagulated by rennet. Hammarstenf has further- 

 more satisfied himself that when solutions of paraglobuline induce 

 coagulation in liquids containing fibrinogen, they owe this property to 

 small quantities of ferment with which they are contaminated; and by 

 using special precautions in their purification, he has found that solu- 

 tions of fibrinogen will coagulate completely on the addition of the fer- 

 ment, when neither liquid contains any trace of paraglobuline, herno- 

 globine, or serum-albumen. 



The coagulation of fibrinogen is, therefore, without doubt due to the 

 action of a ferment. The fibrinogen, as it exists in the circulating 

 blood, is not coa v trulable ; and it becomes so only by contact with the 

 substance which produces its alteration. The only remaining question 

 is in regard to the source of this ferment, when blood is withdrawn from 

 the vessels or coagulates in their interior. The evidence appears to 

 show that it comes from the divided or injured vascular coats, or from 

 the interstitial spaces beyond. The minute quantity necessary to effect 

 coagulation may be exuded from a wounded surface, however small ; 

 and after death it may slowly transude through the membranes, like 

 the coloring matters and serous fluids of the body. But the place and 

 mode of its production can hardly be determined with certainty, until 

 its composition and physical properties are fully known. 



Usefulness of Coagulation. Although the coagulating material of 

 the blood, owing to its small quantity, does not seem to take a large 

 share in nutrition, it is still an important ingredient of the circulating 

 fluid. It is this substance which effects the arrest of hemorrhage from 

 divided or ruptured blood-vessels. Whenever a wound is made in 

 vascular tissues, the blood at first flows freely from the external orifice. 

 But a portion soon coagulates on the edges of the wound, and after a 

 time its successive deposits obstruct the orifice, and prevent further 

 hemorrhage. For wounds of moderate size, in which only veins and 

 capillaries, or small arteries, have been divided, it is sufficient to com- 

 press the wound and to keep its edges in contact for fifteen or twenty 

 minutes. By this time the thin layer of blood between the wounded 

 surfaces has coagulated, and when compression is removed hemorrhage 

 does not reappear. If a large artery be opened, the force with which 

 the blood is expelled prevents local coagulation, or may detach the 



* Hoppe-Seyler, Physiologische Chemie. Berlin, 1879, p. 416. 

 f Archiv fur die gesammte Physiologic. Bonn, 1879, Band xix., pp. 563, 581. 



