RED CORPUSCLES. 141 



a refractive homogeneous appearance. Stained with orange G or eosin 

 it is clear and brightly colored, generally quite unlike any other portion of 

 the specimen. Often the haemoglobin has been more or less dissolved 

 from the corpuscles which then appear granular or reticular. Mean- 

 while the nucleus becomes smaller and so dense as to appear a structureless 

 mass, stained nearly black with haematoxylin. This transformation of the 

 cells is shown in Fig. 165. Cells which are destined to produce red cor- 

 puscles are called erythroblasts, especially in the stages with reticular 

 nuclei. The later stages when the cells are smaller and have dense nuclei 

 are called normoblasts. The nuclei of normoblasts have been seen to be 

 extruded as in Fig. 165. Before they disappear they may become mul- 

 berry, dumb-bell, or trefoil shaped, (as in the group in the lower left hand 

 corner of Fig. 174, p. 152) or they may fragment into several dark masses. 

 These are said to be extruded so that they lie free, outside of the cell, where 

 they are devoured by phagocytes. On the other hand it is believed by 

 some that extrusion never occurs as a 

 normal process, but that the nuclei are 

 dissolved within the cell. The question 

 has long been discussed and is not set- 

 tled. The loss of the nuclei begins in 

 human embryos of the second month; 

 at the third month nucleated corpuscles a 



are still more numerous than the non- FlG ' l6s - TH coR D P uscLEs. MEN ' T F RE 



i L j AiU-iU J ft. J '4, a, Successive stages in the development of 



nucleated. At birth and afterwards It erythroblasts, from a cat embryo; b, 



- .. , . , the extrusion of the nucleus in cat 



is 'unusual to find nucleated red corpus- embryos, 

 cles in the circulating blood. 



The erythroblasts at first divide by mitosis in the blood vessels every- 

 where. Later they gather about the sinusoids of the liver. Apparently 

 they are not only within the blood vessels but also outside of them, in the 

 reticular tissue between the endothelium and the hepatic cells. Red blood 

 corpuscles both nucleated and non-nucleated are flexible bodies incapable 

 of amoeboid movement; accordingly they pass out between endothelial 

 cells less readily than the leucocytes. The emigration of red corpuscles 

 is called diapedesis. In fetal life erythroblasts multiply not only in the 

 liver but also in the spleen. Except in a few mammals the spleen does not 

 normally retain this function in the adult. The red bone marrow becomes 

 the essential permanent location for the production of red corpuscles, 

 and throughout life it contains the multiplying erythroblasts. In certain 

 important diseases normoblasts leave the marrow and occur in the circu- 

 lating blood, sometimes together with large forms having reticular nuclei, 

 and called megaloblasts. The megaloblasts have been regarded as younger 

 erythrocytes than the normoblasts. 



