COAGULATION OF BLOOD. 69 



given, must therefore be taken to represent only an ap- 

 proximate average. 



Coagulation of the Blood. 



When blood is drawn from the body, and left at rest, 

 certain changes ensue, which constitute a kind of rough 

 analysis of it, and are instructive respecting the nature of 

 some of its constituents. After about ten minutes, taking 

 a general average of many observations, it gradually clots 

 or coagulates, becoming solid like a soft jelly. The clot 

 thus formed has at first the same volume and appearance 

 as the fluid blood had, and, like it, looks quite uniform ; 

 the only change seems to be, that the bloodwhich was fluid 

 is now solid. But presently, drops of transparent yellowish 

 fluid begin to ooze from the surface of the solid clot; 

 and these gradually collecting, first on its upper surface, 

 and then all around it, the clot or " crassamentum" dimin- 

 ished in size, but firmer than it was before, floats in a 

 quantity of yellowish fluid, which is named serum, the 

 quantity of which may continually increase for from 

 twenty- four to forty- eight hours after the clotting of the 

 blood. 



The changes just described may be thus explained. The 

 liquor sanguinis, or liquid part of the blood, consists of 

 serum, holding fibrin in solution.* The peculiar pro- 

 perty of fibrin, as already said, is its tendency to become 

 solid when at rest, and in some other conditions. When, 

 therefore, a quantity of blood is drawn from the vessels, 

 the fibrin coagulates, and serum and blood corpuscles are 

 held, or, as it were, soaked and entangled in the solid 

 substance which it forms. 



But after healthy fibrin has thus coagulated, it always 



* This statement has been left unaltered in the text ; but, as will be 

 ssen farther on, it requires some modification. (Eo.) 



