THE RED BLOOD CORPUSCLES 



173 



dumb-bell.^ Its thin central area is surrounded by a thick marginal 

 zone. When the latter is brought into focus, the center appears dark, 

 because its focal point lies at this time at a lower level. When cir- 



FiG. 97a. — Human Red Corpus- 

 cle Placed Flat and on Edge. 



Fig. 975. — Red Corpuscle of Frog 

 Placed Flat and on Edge. 



culating through the vascular channels, the fully developed red cell 

 does not contain a nucleus; in fact, the loss of this constituent very 

 shortly after the cell has entered the blood-vessels, is generally con- 



Fig. 98. — Area of Capillaries. 

 Showing tubules of different diameter, some so small that the red cells cannot enter 

 at all and others through which they can only pass by assuming an elliptical outline. 



sidered as the cause of the central depression. In the camels, the red 

 corpuscle presents an elliptical outline, but resembles the preceding 



1 Weidenreich, Lewis, Radasch and others hold that the red corpuscles assume 

 this shape only in shed blood and are cup-shaped or bell-shaped while circulating. 

 This change is said to be caused by cooling and evaporation. Jordan, who has 

 reinvestigated this subject more recently, states that a freely moving corpuscle 

 always shows a central depression. (Proc. Soc. Exp. Biol, and Med., xii, 1915.) 

 Viewed from the side, however, these biconcave discs give the impression of shallow 

 oups, because the pressure tends at times to cause them to bulge out centrally. 



