MITOSIS IN CENTRAL NERVOUS SYSTEM 549 
All the figures are from frontal sections of the cord and brain of the albino rat. 
Figs. 1 to 4 Diagrammatic drawings of frontal sections through the cervical 
cord and at three different levels of the cerebrum of a one-day-old rat. Each 
figure shows the position of a dividing cell in the section of the series corresponding 
to that number. The dotted lines outline gray matter. The ventral portion of 
the tissue appears at the bottom. 
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Fig. 1 Distribution of the dividing cells in ten consecutive sections of the cer- 
vical cord at the level of its greatest area. 75. 
As to the portions of the central nervous system studied. At 
first examination was made at various levels throughout the length 
of the cord, cerebellum and cerebrum to determine whether mito- 
sis was limited to a particular locality. Then, in order to deter- 
mine numerical relationships, attention was focussed upon cer- 
tain definite levels. For the spinal cord, the sections showing 
greatest area in the cervical, thoracic and lumbar levels; for the 
cerebellum, sections passing through the region showing greatest 
area, and for the cerebrum sections passing through the optic 
chiasma were chosen. In each instance frontal sections were 
used. The number of sections thus studied varied a little— 
in the cord at least ten and frequently more: in the brain at 
least five and frequently more. 
