PLASMA. 



221 



PLASMA. 



The fluid part of the blood is of a pale straw color, when pure 

 and free from the coloring matter of the blood corpuscles, and of 

 slightly less density than the blood corpuscles (p. 218). Ex- 

 cept special precautions are taken, the plasma is altered when 

 removed from the blood vessels and coagulation of the blood takes 

 place ; so that, under ordinary circumstances, plasma does not 

 come under observation, except when the constitution of the blood 

 is revealed by the microscope. It was first separated from the cor- 



FIG. 96. 



Reticulum of Fibrin Threads after staining has made them visible. The network (b) 

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



puscles by the filtration of frog's blood, to which had been added 

 strong syrup, which checks coagulation and spoils the flexibility 

 of the corpuscles, so that they are caught in the meshes of the 

 filter, and the clear plasma passes through. 



To obtain mammalian plasma, free from corpuscles, it is neces- 

 sary to use some other method, as the small elastic corpuscles 

 easily run through the meshes of the thickest filter paper. 



The blood of the horse is chosen because it coagulates more 



