1019 
compare  briefly  the  results  arrived  at  by  some  of  the  previous 
investigators  of  this  subject.  The  latter  have,  however,  worked  with 
myelins  sheath  staining  methods  and  have  determined  the  number 
of  medullated  nerve  fibres  in  different  States. 
Dunn  ’)  “A  considerable  increase  in  the  nnmber  of  medullated 
nerve  fibres  occurs  during  the  early  life  of  the  albino  rat”.  Dunn 
investigated  the  ventral  root  of  6* *11  in  Mus  noriveg.  albinus.  The 
same  thing  is  true,  according  to  Hatai  'O  of  the  “albino  rat”  with 
regard  to  the  ventral  roots  of  CVI,  7’AIV  and  LII,  and,  according 
to  Boughton ’),  with  regard  to  n.  occulomotorius  in  the  same  animal. 
Boüghton’s  investigations  (06)  about  cognate  problems  in  the  cat  and 
WiLLEMs’s  “)  in  the  rabbit  point  to  the  same  conclusion. 
Dunn  States:  “Ranson’s  records  then  are  comparable  with  those 
presented  now,  and  together  tliey  show  that  in  regard  to  the  second 
spinal  nerve  of  the  albino  rat  the  number  of  medullated  nerve  fibres 
in  both  the  dorsal  and  ventral  nerve  roots  increases  during  the  life 
of  the  indi\'idual,  but  that  the  greatest  increase  occurs  before  the 
sexual  malurity  or  so-called  puberty  of  the  animal,”  and  so  on.  It 
is  thus  shown  that  what  is  true  in  this  respect  for  all  the  axons  — 
as  shown  by  the  results  of  the  calculations  given  in  the  above  table — 
is  also  true  for  only  the  medullated  nerve  fibres.  The  percentage  of 
increase  obtained  by  using  myelin  sheath  staining  methods  on  the 
material  in  question  is  considerably  larger  than  that  arrived  at  by 
impregnation  of  the  axons.  This  is  due  to  the  fact  that  the  young 
animal  has  relatively  considerably  more  axons  free  from  medullary 
sheaths  than  the  older  one.  This  increase  in  the  number  of  nerve 
fibres  is  decidedly  larger  in  the  dorsal  than  in  the  ventral  roots,  a 
fact  which  is  seen  most  clearly  when  the  comparison  is  based  on 
the  conditions  in  a rather  large  number  of  animals.  This  is  not  so 
striking  in  Canis,  and  Mus  rattus  shows  an  entirely  reversed  state 
of  affairs.  These  apparent  exceptions  are,  however,  probably  due  to 
1)  Dunn,  Elisabeth  Hopkins.  The  influence  of  age,  sex,  weight  and  relation- 
ship  upon  the  number  of  medullated  nerve  fibres  and  on  the  size  of  the  largest 
fibres  in  the  ventral  root  of  the  second  cervical  nerve  of  the  albino  rat.  The 
Journ.  Comp.  Neur.  Vol.  22.  N'^.  2.  1912. 
*)  Hatai,  Shinkiski.  On  the  increase  in  the  number  of  medullated  nerve  fibres 
in  the  ventral  roots  of  the  spinal  nerves  of  the  growing  white  rat.  J Comp.  Neur. 
Vol.  13,  1903. 
Boughton,  Thomas  Harris.  The  increase  in  the  number  and  size  of  the 
medullated  fibres  in  the  occulomotor  nerve  of  the  white  rat  and  of  the  cat  at 
different  ages.  J.  Comp.  Neur.  Vol.  16.  1906. 
WiLLEMS,  Edouard.  Localisation  motrice  et  kinesthesique.  Les  noyaux 
masticateur  et  mesencephalique  du  trijumeau  chez  Ie  lapin.  Le  Neuraxe  t.  12,  191 1. 
66* 
