THE RED GIvOBUIvES : ERYTHROCYTES. 



These have a different origin in successive stages of life. In 

 the very early embryo they are found in groups in the mesoderm. 

 In this early life, in many mammals, all the red globules are nu- 

 cleated. At a more advanced stage, but still in the early embryo 

 they are found in great numbers in the liver and lymph nodes as 

 the second point of origin. In the fully developed embryo they 

 are formed mainly in the liver and spleen. In extra- uterine life 

 they are formed in the red bone marrow. 



Form, The embryonic red globule, beside being often nucle- 

 ated, is not usually disc shaped. The red blood globule of extra- 

 uterine life is usually described as a flattened disc, but Lowen- 

 hoeck, Rindfleisch, Weidenreich and I,ewis claim that this is a 

 post mortem distortion, and that the real form of the live cor- 

 puscle, as examined in the fresh or circulating blood, is that of 

 a cup, or a hollow sphere with an opening at one side. The 

 absence of a nucleus from the adult red corpuscle further sug- 

 gests that the central space and the opening are the result of the 

 loss of the nucleus of the spherical red globule of the embryo. 

 In shed blood the red globules shrink into round disc-shaped 

 bodies concave on each of the flattened sides, and with a tendency 

 to accumulate in rouleaux like a roll of coins. 



Size. The red globules vary in size from 6j«. to 9/x in diameter, 

 the average being about 7j«.. Where the smallest (microcytes, 

 2-5/i) and large (megalocytes, 9-12/*,) are found in the same speci- 

 men, the microcytes, are doubtless largely young cells, though 

 there are also cases associated with loss of blood or pernicious 

 anaemia, which would tend to dilution of the blood and expan- 

 sion of the globules. Other things being equal, the density of 

 the plasma would contract the globules and the dilution of the 

 plasma would enlarge them. 



Hemoglobin. A reduction of the coloring matter (hsemaglo- 

 bin), so that the central clear area is largely encreased, is a com- 

 mon condition in anaemia. 



Distortion of the Red Cells (^Poikilocytosis') is not uncommon. 

 It may be mere crenation (indentations) of the margin, or as a 

 510 



