248 



MANUAL OF PHYSIOLOGY. 



person during fever then the heavier red corpuscles have time 

 to subside to the lower layers of the clotting plasma, while the 

 white cells are caught in the meshes of the fibrin and remain in 

 the upper layer of the clot, which then has the pale color familiar 

 to the physician in the old days of bleeding as the " buffy coat," 

 or crusta phlogistica. This buffy coat contains a greater proportion 

 of the elastic fibrin and soft white cells than the rest of the clot, 

 and incloses but few red corpuscles, therefore the fibrin can con- 

 tract more completely in this upper layer than in the deeper part 



FIG. 109. 



Eeticulnm of Fibrin Threads after staining has made them visible. The network (6) 

 appears to start from granular centres (a). (Ranvier.) 



of the clot, which includes the red corpuscles. The effect of this 

 is, that the upper surface becomes concave, and a "cupped " clot 

 is formed. The contraction of the clot proceeds for days, and in 

 order to see the characters described above, the blood should be 

 kept in a cool place and perfectly motionless. 



The contraction of the fibrin and separation of the serum can 

 be made to take place much more quickly by gentle agitation 

 causing the ends of the fibrin threads to separate from the sides 

 of the vessel, but by thus .disturbing the clot, during its forma- 



