Metazoa Rana. 



283 



on being examined under the microscope is found to consist 

 of an almost colourless medium or plasma in which floats an 

 immense number of blood-corpuscles of two kinds the one 

 irregular in shape, colourless, and not unlike Amotbce in 



FIG. 146. BLOOD-CORPUSCLES OF THE FROG. (Ranvier.) 



a, red corpuscles seen on the flat ; v, vacuoles in a corpuscle ; t>, c, red 

 corpuscles seen in profile ; n, k, colourless corpuscles at rest ; in, colour- 

 less corpuscle showing pseudopodia ; /, coloured fusiform corpuscle. 



general appearance, and exhibiting when living that 

 indefinite motion which has already been described and 

 termed amoeboid ; the other definite and elliptical in shape 

 and reddish yellow in colour. It is from these latter that 

 the blood derives its red colour. 

 Blood after death, or if with- 

 drawn from the living body, does 

 not long remain liquid. In 

 the plasma extremely delicate 

 branched filaments (fibrin threads) 

 make their appearance, in the 

 meshes of which the corpuscles 

 become entangled. The clot (coagulum) subsequently con- 

 tracts, with the result that the watery element (serum) of 



FIG. 147. FIBRIN THREADS. 

 (Schafer.) 



The coloured corpuscles have 

 been removed by washing. 



