THE CESSATION OF MITOSIS IN THE CENTRAL 
NERVOUS SYSTEM OF THE ALBINO RAT 
EZRA ALLEN 
From the Philadelphia School of Pedagogy and The Wistar Institute of Anatomy and 
Biology 
TWENTY-TWO FIGURES 
: INTRODUCTION 
While different observers have recorded the fact that mitosis 
continues in the central nervous system after birth in mammals 
which are relatively immature when born, the exact period of 
its cessation In any one such animal does not seem to have been 
determined. The purpose of this paper is to record results of 
studies which I have been pursuing, with many interruptions, 
for three years, in the effort to discover how long cell division 
may continue after birth in the central nervous system of the 
albino rat. 
The literature on this phase of vertebrate growth is not exten- 
sive. Buchholtz (90) records mitoses in all parts of the central 
nervous system of new-born dogs and rabbits and those a few 
days old. Sclavunes (’99) states that in new-born dogs, cats 
and white mice dividing cells are to be found in the wall of the 
central canal of the cord, in its white substance, in the sub- 
stantia gelatinosa, in the anterior gray horns, at the point of 
entrance of the dorsal and ventral nerve roots, ‘among the cells - 
of the spinal ganglia,” in the dorsal and ventral septa of the 
cord, in the dura, and “‘abundantly”’ in the arachnoid and under 
the pia. Hamilton (’01) found mitoses in the cerebrum and spinal 
cord of the albino rat in animals four days old. Addison (11), 
in his study of the Purkinje cells of the same animal, notes mitoses 
regularly occurring in the cerebellar cortex at twenty-one days, 
and in one individual at twenty-two days after birth. 
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