SECT. 1. THE COAGULATION OF BLOOD. 



Blood, when shed from the blood-vessels of a living body, is 

 perfectly fluid. In a short time it becomes viscid; it flows less 

 readily from vessel to vessel. The viscidity increases rapidly until 

 the whole mass of blood under observation becomes a complete 

 jelly. The vessel into which it has been shed, can at this stage be 

 inverted without a drop of the blood being spilt. The jelly is of : 

 the same bulk as the previously fluid blood, and if forcibly removed, - 

 presents a complete mould of the interior of the vessel. If the 

 blood in this jelly stage be left untouched in a glass vessel, a few 

 drops of an almost colourless fluid soon make their appearance on 

 the surface of the jelly. Increasing in number, and running 

 together, the drops after a while form a superficial layer of pale 

 straw-coloured fluid. Later on, similar layers of the same fluid are 

 seen at the sides and finally at the bottom of the jelly, which, ^ 

 shrunk to a smaller size and of firmer consistency, now forms a 

 clot or crassamentum, floating in a perfectly fluid serum. The 

 shrinking and condensation of the clot, and the corresponding 

 increase of the serum, continue for some time. The upper surface 

 of the clot is generally cupped. A portion of the clot examined 

 under the microscope is seen to consist of a feltwork of fine granular 

 fibrils, in the meshes of which are entangled the red and white 

 corpuscles of the blood. In the serum nothing can be seen but a 

 few stray corpuscles. The fibrils are composed of a substance 

 called fibrin. Hence we may speak of the clot as consisting 

 of fibrin and corpuscles ; and the act of clotting or coagulation is 

 obviously a conversion of the naturally fluid portion of the blood 

 or plasma into fibrin and serum, followed by separation of the 

 fibrin and corpuscles from the serum. 





