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THE STORY OF THE RED BLOOD CORPUSCLES. 113 
of these cells, the ordinary nucleated red corpuscles, differs in 
important respects from the marrow cells. They vary con- 
siderably in size, Some are of the same size as ordinary 
red corpuscles, others are considerably larger, and all inter- 
mediate sizes may be found. The protoplasm of these cells 
is tinged more or less deeply with hemoglobin, and is 
entirely free from granules, and in both respects presents a 
marked contrast to that of the marrow cells. The nucleus 
is quite circular, and stains very deeply on account of the 
great density of the chromatin network. The cells differ 
somewhat among themselves. When a large number of cells 
is examined, it is possible to make out that these differences 
depend upon age. The youngest cells are the largest. In 
them the protoplasm is comparatively scanty, and the 
hemoglobin tints it very faintly. The nucleus is pro- 
portionately large, and has a distinct chromatin network. 
These cells undergo active subdivision. 
As the cells get older they become smaller owing to their 
repeated subdivisions. The protoplasm becomes more deeply 
coloured with hemoglobin. The nucleus, also, becomes 
small, dense, homogeneous in structure, and stains very 
intensely with nuclear dyes. These may be regarded as 
signs of age. 
From the appearance presented by these older nucleated 
red corpuscles there can be no doubt that they give rise to 
the ordinary red cells by the loss of their nuclei. How this 
change comes about is by no means certain, and in spite of 
‘a great deal of lively discussion, the fate of the nucleus still 
remains something of a mystery. Some writers believe that 
the nucleus is extruded, and either disappears by disintegra- 
tion in the blood, or, by the aid of a small remnant of proto- 
plasm which surrounds it, gradually forms a new nucleated 
red corpuscle. The latter theory (that of Rindfleisch) is not 
probable, as the nucleus in the older corpuscles has all the ap- 
pearances of age. Extruded nuclei may be found in sections 
and other preparations, and this favours the view of their exit 
from the protoplasm, whatever their ultimate fate may be. 
Some observers (Pappenheim, Israel) believe that the nuclei 
undergo disintegration and absorption within the corpuscles, 
and explain the occurrence of nuclei without protoplasm as 
VOL. II. 
