THE RED BLOOD CELL 



205 



cation by extrinsic factors. The erythroplastid is of course a very 

 delicate structure, and slight tractions or tensions incident to passage 

 through exiguous confines, or osmotic currents set up in fixing fluids, 

 or the coagulation of its protoplasm, would produce modifications and 

 distortions. Almost any conceivable mechanical modification would of 



FIG. 218. FROM A FRESHLY PREPARED, UNSTAINED SPECIMEN OF HUMAN BLOOD. 



Three leukocytes, an eosinophil, a polynuclear, and a lymphocyte, are represented. 

 Many red blood corpuscles (erythroplastids), some on the flat, some in rouleaux 

 and in profile, are also shown. X 1200, but reduced somewhat in reproduction. 

 (After Schafer.) 



necessity change a circular biconcave disk into some sort of cup-shaped 

 element. 



The red blood element lacks a nucleus, hence the propriety of in- 

 sistence on the term 'plastid' or 'corpuscle' in preference to cell (cyte). 

 The red elements of all mammals are non-nucleated. The lower forms 

 have nucleated elements (erythrocytes), frequently of ellipsoidal form. 

 Mammalian red elements of greatly divergent sizes (2.5 /u. in musk ox; 

 9.4 /u, in elephant ; dog, 7.5 /u, ) are all of circular outline, except those 

 of the camelidge (llama, camel, etc.) which are elliptical. The erythro- 

 plastids are generally believed to be enclosed by a delicate membrane, and 



