COAGULATION. 433 



some active thrombin is circulated through a living liver it loses 

 its power of inducing coagulation in solutions containing fibrinogen. 

 Its thrombin has been destroyed or made inactive by some effect 

 of the liver, and it is possible, although not demonstrated as yet, 

 that the liver may exercise such a protective action under special 

 circumstances during life. That this supposed action of the liver 

 is not always essential is shown by the fact that in animals from 

 whom the liver has been Removed experimentally the blood does 

 not clot within the vessels. The older observers were impressed 

 w r ith the fact that blood remains uncoagulatcd for long periods if 

 kept in contact with w 7 hat may be called its normal surface, that 

 is, the interior of the heart or blood-vessels. In an excised heart 

 or blood-vessel the blood, although at rest, remains fluid for a long 

 time. It was thought possible, therefore, that the normal en- 

 dothelial walls of the vessels exercise a restraining influence of 

 some kind upon the coagulation of the blood. In recent times 

 this view has taken the form, corresponding to the knowledge of 

 the day, of a suggestion that an antibody namely, an anti- 

 thrombin exists in the blood and actively retards or prevents co- 

 agulation. While some authors (Morawitz) believe that such an 

 antithrombin exists normally in circulating blood and is essential 

 in maintaining its fluidity, others (Schmidt) hold to the view that 

 substances retarding coagulation are liberated only from the dis- 

 integration of the cellular elements and are present practically, 

 therefore, only in the shed blood. Loeb* has not been able to 

 detect the existence of an antithrombin in extracts of the inner wall 

 of the blood-vessels. It would seem to be premature to accept 

 the view that under normal conditions there exists in the blood any 

 substance that retards or prevents coagulation, although under 

 artificial or unusual conditions, as stated in the next paragraph, 

 such substances may be produced. 



Intravascular Clotting. As is well known, clots may form 

 within the blood-vessels in consequence of the introduction of for- 

 eign material of any kind. Air, for instance, that has gotten into 

 the veins, if not absorbed, may act as a foreign substance and 

 cause the same chain of events as when the blood is shed, namely, 

 the disintegration of formed elements, formation of thrombin, and 

 clotting. So also when the internal coat of a blood-vessel is in- 

 jured as, for instance, by a ligature the altered endothelial cells 

 act as a foreign substance. If the circulatory conditions are favor- 

 able for instance, if the ligated artery causes a stasis of blood at 

 that point there may be an agglutination of the blood plates, 

 starting at the injured surface, and the subsequent formation of a 

 clot. Intravascular clotting may also be produced by the injection 



* Leo Loeb, u Virchow's Archiv," 176, 10, 1904; also " Hofmeister's Bei- 

 trage," 5, 534, 1904. 

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