THE PLASMA 159 



chief bulk, and fibrino- globulin which remains in solution and is formed only 

 in small quantity (Hammarsten). 



The difficulties with which the subject of coagulation : a beset, and which 

 we have been able to discuss here only in a cursory manner, are still more 

 multiplied when we ask why the blood does not dot in the vessels. That the 

 constant movement of the blood is not the reason is proved by the fact that 

 blood coagulates outside the body more rapidly when it is stirred. Cooling 

 of the blood cannot account for coagulation, for it is possible to postpone 

 the process for a long time by this very means. Neither can contact with the 

 air be considered, for coagulation goes on in the usual manner if blood is 

 collected (over mercury) by exclusion of air. 



Coagulation does not occur if the blood is drawn by means of an oiled 

 cannula, or if it is caught in an oiled vessel: in fact it can now be stirred 

 with an oiled rod without producing coagulation. But if it is stirred with 

 an ordinary rod, or if small solid particles be introduced, coagulation takes 

 place immediately (Freund). The reason why coagulation does not take 

 place under the above-mentioned circumstances doubtless lies in the fact that 

 the blood is prevented by the oil from coming in contact with the wall of 

 the vessel. Attempts have been made to explain the absence of coagulation 

 in the blood vessels in a similar manner, by assuming that in health the 

 necessary adhesion of the blood to the walls is wanting. When the endothelial 

 lining of the vessels becomes abnormally changed in any way so that internal 

 adhesion occurs, intravascular clotting ensues. Against this conception how- 

 ever it may be objected that the blood always thoroughly wets the internal 

 wall of the blood vessels (B. Lewy). 



Beautiful examples of the inhibiting property of the vascular walls are 

 found in the facts that blood remains fluid for a long time in a section of a 

 vein ligated off at both ends (Hewson) : and that a turtle's heart filled with 

 blood beats for days without any clotting if the temperature of the contained 

 blood be low (Briicke). 



Opinions differ considerably as to the real nature of the changes produced 

 by adhesion of the blood to rough surfaces, so that at this time we are unable 

 to form any definite conception of the matter. But since substances have 

 been found in the blood which exercise an inhibiting influence on coagulation, 

 it is at least conceivable that during life and with uninjured vascular walls, 

 the inducing and inhibiting bodies neutralize each other, while in shed blood 

 the former preponderate and thus bring about coagulation. 



In the living body the coagulability of the blood can be abolished by intra- 

 vascular injection of albumoses ( Schmidt-Miihlheim,. Fano) or of leech ex- 

 tracts (Haycraft). If the blood is diverted from the liver and the intestine 

 so that it circulates only through the extremities, the head and the lungs, it 

 likewise loses its ability to coagulate. 



Coagulation of the blood is of extremely great importance as a means of 

 protection for the body, since bleeding from injured vessels, unless they be too 

 large, is thereby stopped. If the blood did not coagulate every slight injury 

 would involve great loss of blood. When the larger vessels are ruptured coagu- 

 lation does not suffice : for the blood flows out in such quantity and with such 

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