1045 
days  old  he  found  (counting  in  mm* *)  46  mitoses  in  the  cervical, 
75  in  the  thoracic  and  14  in  the  lumbar  region,  but  that  in  an 
aninml  twenty  days  old  he  could  not  show  a single  one. 
Hamilton ')  found  in  thirteen  succeeding  sections,  6,75  thiek, 
from  the  niedulla  spinalis  of  a four  days  old  rat  mitoses  in  the 
ependyma  and  64  situated  extraventricularly. 
Addison  W.  H.  F.’)  found  in  au  “albino  rat”  nearly  22  days  old 
mitoses  “in  the  other  granule  layer”  of  the  cerebellum. 
ScLAVUNOS  G.  ‘)  bas  observed  mitoses  in  the  central  nerve  system 
of  new-born  dogs. 
SuGiTA  Naoki  ^),  vvho  has  studied  the  post-embryonic  growth  of 
the  cortex  of  the  brain  in  the  “albino  rat”,  found  that  the  value 
for  the  number  of  cells  in  this  region  in  the  ten  days  old  animal 
was  1,9  X the  value  at  birth,  and  that  the  number  of  cells  increases 
further  during  the  next  ten  days  and  is  complete  at  twenty  days. 
After  this  time  the  number  of  cells  is  practically  constant  and  the 
number  of  cells  in  the  fully-grown  state  is  approximately  twice  as 
great  as  at  birth.  These  calculations  are  based  on  the  determination 
of  the  number  of  cells  in  onlj  two  layers  at  only  ojie  place  and 
therefore  their  general  value  may  be  questioned.  S.  has,  however, 
previously  shown  by  measurements  made  at  different  places  on  the 
cortex  of  the  brain  that  it  undergoes  the  same  relative  increase  in 
thickness  between  birth  and  maturity.  S.  considers  that  the  values 
obtained  may  therefoie  with  great  probability  be  generalized  for  the 
whole  cortex.  With  regard  to  the  way  in  which  such  a post-em- 
bryonic increase  in  the  number  of  cells  in  the  cortex  takes  place 
one  can,  of  course,  herein  supported  by  Allen,  who  in  25  days 
old  specimens  of  the  “Albino  rat”  found  as  many  as  27  mitoses 
per  mm®  of  tissue  in  the  cerebrum,  consider  that  it  is  due  to 
mitolic  division. 
The  values  given  for  the  number  of  mitoses  and  for  the  increase 
in  number  of  the  cells  in  the  central  nervous  system  do  not  refer 
to  any  definite  number  of  cells,  but  apply  to  all  the  cells  taken 
together,  and  thus  do  not  exclude  an  increase  in  the  number  of 
b Hamilton,  Alice,  The  division  of  differential  cells  in  the  central  nervous 
system  of  the  white  rat.  J.  Gomp.  Neur.,  Vol.  II,  pp.  297 — 320,  1901. 
b Addison,  W.  H.  F.,  The  development  of  the  Purkinje  cells  and  of  the  cortical 
layers  in  the  cerebellum  of  the  Albino  raf.  J.  Gomp.  Neurol.  Vol.  21,  pp.  459— 487. 
*)  ScLAVUNOS,  G.,  lleber  Keimzellen  in  der  weissen  Substanz  des  Rückenmarks 
von  alteren  Embryonen  und  Neugeborenen 'Anat.  Anz.,  Bd.  16,  1899. 
b SuGiTA  Naoki,  Gomparative  Studies  on  the  growth  of  the  Cerebral  cortex 
III,  IV  and  VI,  Journ.  Comp.  Neur.  Vol.  29,  1918, 
