58 THE HUMAN BODY. 



corpuscles or both, we have still the problem why, under 

 normal conditions, do not these break down in the circulating 

 blood : have perchance the blood-vessels some part in the 

 matter ? 



Relation of the Blood-vessels to Coagulation. As to 

 the role of the blood-vessels with respect to coagulation, two 

 views are held, between which the facts at present known do 

 not permit a decisive judgment to be made; and there may 

 be some truth in both. One theory is that the vessels actively 

 prevent coagulation by constantly absorbing from the blood 

 some substance, as the fibrin-ferment, the presence of which 

 is a necessary condition for the formation of fibrin and which 

 is supposed to be constantly forming in the blood, but to be 

 as steadily removed from it or destroyed by the lining cells of 

 the blood-vessels. In support of this opinion is brought for- 

 ward the fact that it is possible to inject considerable quanti- 

 ties of a solution of fibrin-ferment into the blood of a living 

 animal without causing intravascular coagulation. 



The other view is that the blood-vessels are passive. They 

 simply do not excite those changes in the blood constituents 

 which give rise to the formation of fibrin-ferment, while 

 foreign bodies in contact with the blood do excite these 

 changes and so lead to coagulation. In support of this view 

 are brought forward the facts that drawn blood clots faster in 

 vessels of such shapes that a large surface of blood is exposed 

 to foreign contact; and that coagulation takes place rapidly 

 in a vessel with a rough interior, while in a chemically clean 

 glass vessel it occurs slowly. The experiment already men- 

 tioned of getting a clot around a thread passed through a blood- 

 vessel, and also that of getting extensive clotting within the 

 blood-vessels by the injection into a vein of extract of the 

 thymus body, may be cited as tending to show that the linings 

 of the blood-vessels cannot actively prevent coagulation; but 

 it may be objected that in the one case locally s and in the other 

 generally, the ferment is set free in the blood so fast that the 

 vessels cannot remove it in time to prevent the formation of 

 fibrin. Blood poured out from a torn vessel among other 

 tissues of the body often clots very slowly; this may be due 

 either to the tissues in general possessing the power of de- 

 stroying fibrin-ferment or to their being merely indifferent 

 substances not exciting the changes which lead to fibrin 

 formation. 



