CH. XXIX.] 



COAGULATION OF THE BLOOD 



447 



be obtained from blood by whipping it with a bunch of twigs ; the 

 fibrin adheres to the twigs and entangles but few corpuscles ; these 

 may be removed by subsequent washing with water. 



FIG. 317. Reticulum of fibrin, from a drop of human blood, after treatment with rosanilin. The 

 entangled corpuscles are not seen. (Ranvier.) 



Serum is plasma minus the fibrin which it forms. The relation 

 of plasma, serum, and clot can be seen at a glance in the following 

 scheme of the constituents of the blood : 



Blood 



Plasma 



/Serum 

 IFibriir 



Clot 



.Corpuscles 



It may be roughly stated that in 100 parts by weight of blood 60-65 

 parts consist of plasma and 35-40 of corpuscles. 



The huffy coat is seen when blood coagulates slowly, as in horse's 

 blood. The red corpuscles sink more rapidly than the white, and 

 the upper stratum of the clot (buffy coat) consists mainly of fibrin 

 and white corpuscles. 



Coagulation is hastened by 



1. A temperature a little over that of the body. 



2. Contact with foreign matter. 



3. Injury to the vessel walls. 



4. Agitation. 



5. Addition of calcium salts. 



6. Injection of nucleo -protein into the circulation causes intra- 



vascular clotting. 



Coagulation is hindered or prevented by 

 1. A low temperature. In a vessel cooled by ice, coagulation 



may be prevented for an hour or more. 



