COAGULATION OF THE BLOOD. 



227 



Fig. 64. 



come more numerous. They run together and coalesce with each 

 other, as more and more fluid exudes from the coagulated mass, 

 until the whole surface of the clot is covered with a thin layer of 

 fluid. The clot at first adheres pretty strongly to the sides of the 

 vessel into which the blood was drawn ; but as its contraction goes 

 on, its edges are separated, and the fluid continues to exude between 

 it and the sides of the vessel. This exudation 

 continues for ten or twelve hours ; the clot 

 growing constantly smaller and firmer, and 

 the expressed fluid more and more abundant. 

 The globules, owing to their greater con- 

 sistency, do not escape with the albuminous 

 fluids, but remain entangled in the fibrinous 

 coagulum. Finally, at the end of ten or 

 twelve hours the whole of the blood has 

 usually separated into two parts, viz., the clot Bowl of 

 which is a red, opaque, dense and resisting BI.OOD, after twelve hours; 



<_ . showing the clot contracted 



semi-solid mass, consisting of the fibrin and ami floating in the fluid serum, 

 the blood-globules ; and the serum, which is a 



transparent, nearly colorless fluid, containing the water, albumen^ 

 and saline matters of the plasma. (Fig. 64.) 



The change of the blood in coagulation may therefore be ex- 

 pressed as follows : 



Before coagulation the blood consists of 



1st. GLOBULES ; and 2d. PLASMA containing 



Fibrin, 

 Albumen, 

 Water, 

 [ Salts. 



After coagulation it is separated into 



r Albumen, 



1st. CLOT, containing | ! " * x and 2 d. SERCM, containing ] Water, 



' Salts. 



The coagulation of the blood is hastened or retarded by various 

 physical conditions, which have been studied with care by various 

 observers, but more particularly by Robin and Yerdeil. The con- 

 ditions which influence the rapidity of coagulation are as follows : 

 First, the rapidity with which the blood is drawn from the vein, 

 and the size of the orifice from which it flows. If blood be drawn 

 rapidly, in a full stream, from a large orifice, it remains fluid for a 

 comparatively long time ; if it be drawn slowly, from a narrow 

 orifice, it coagulates quickly. Thus it usually happens that in the 

 operation of venesection, the blood drawn immediately after the 



