1047 
System.  Among  the  investigators  who  have  made  siieh  observations 
we  quote  Rbtzius,  v.  Gehuchten,  Ramon  y Cajau,  Dejkrine. 
The  presence  of  degenerating  nerve  elements  in  individuals  tliat 
are  growing  also  readers  the  possibility  of  a regeneralion  of  such 
very  probable.  If  there  is  no  i-egeneration,  tlie  nerve  elements  woiild, 
of  cotirse,  decrease  during  grovvtli — a phenomenon  tliat  is  not  indi- 
cated  by  any  recorded  observations.  The  probability  of  getieration 
becomes  certainty,  however,  when  one  investigates  suitable  pre|)a- 
rations  from  the  central  nervoiis  system,  for  instance  from  the 
spinal  cord  of  animals  at  varions  post-embryonic  ages.  Such  pre[)a- 
rations  show  numerous  figures  of  new  growtb,  which  seem  to  me 
sufficiënt  to  explain  not  only  how  degenerated  gang  lion  cel  Is 
are  replaced,  but  also  how  the  increase  in  nerve  fibres  in  the 
central  roots  arises,  which  I proved  above  to  exist  during  the  period 
of  growth. 
I have  made  suitable  preparations  for  these  investigations  from 
the  spinal  cord  of  toads,  mice,  rats  and  dogs  of  different  post-em- 
bryonic ages.  The  material  was  tixed  either  in  Flemming’s  or  Zenker’s 
tixing  liquids  and  the  paraffin  sections  ent  from  it  were  impregnated 
either  with  Heidenhain’s  iron-alum  hoematoxylin  or  with  Erlich’s 
acid  iKjernatoxylin.  I have  in  addition,  quite  excellent  Bielschowsky- 
preparations  from  this  material. 
In  the  hcematoxylin-impregnated  preparations  from  toads  2 cm. 
long  (from  neck  to  sacruin)  and  ten  days  old  mice  I found  some 
— but  very  few  — mitoses.  On  the  other  hand  I have  not  found 
any  certain  examples  of  such  mitoses  in  the  older  individuals  of  this 
species  nor  in  six  and  seventeen  days  old  dogs  or  in  full-grown 
ones.  In  a young  mouse  23  days  old  {Muf>  musc.  var.  alhus)  I found 
three  appearances,  which  are  reproduced  in  figs.  9 and  11.  The 
figures  are  carefully  drawn  from  preparations  — which  are  from 
the  material  that  was  tixed  by  Flemming’s  method  — and,  at  the 
first  glance,  certainly  produce  the  impression  of  being  mitoses,  and 
it  is  possible,  of  course,  that  this  is  the  case.  A number  of  facts 
seem  to  me,  however,  to  render  this  doubtful;  these  are  first,  that  I 
have  not  found  any  more  mitoses  in  this  animal  and,  secondly,  that  in 
other  mice  of  equal  age,  in  which  the  material  was  fixed  according  to 
Zenker’s  method  — - this  method  gave  better  and  finer  results  — 
and  impregnated  in  the  same  way,  I have  not  found  any  tracé  of 
mitoses.  In  any  case  I have  not  found  any  appearance  of  amitosisin  pre- 
paratipns  of  the  spinal  cord  of  white  mice  more  than  24  days  old. 
My  observations  of  mitoses  in  the  spinal  córd  of  growing  individuals 
thus  agree  on  the  whole  with  those  {irevionsly  made  by  other  in- 
