﻿30 
  Dr. 
  H. 
  Eltringham 
  on 
  Butterfiy 
  Vision. 
  

  

  and 
  hydration 
  of 
  the 
  sections 
  they 
  are 
  placed 
  in 
  1| 
  % 
  

   silver 
  nitrate 
  and 
  exposed 
  to 
  bright 
  sunhght 
  for 
  ten 
  

   minutes, 
  washed 
  in 
  distilled 
  water, 
  and 
  placed 
  in 
  1 
  % 
  

   gold 
  chloride 
  for 
  two 
  minutes 
  in 
  a 
  bright 
  light, 
  washed 
  

   again 
  and 
  placed 
  in 
  aqueous 
  solution 
  of 
  pyrogallic 
  acid 
  

   to 
  complete 
  the 
  reduction. 
  

  

  I 
  have 
  given 
  this 
  process 
  at 
  length 
  because 
  other 
  workers 
  

   may 
  find 
  it 
  useful 
  for 
  brain 
  tissues. 
  For 
  eye 
  work 
  I 
  have 
  

   not 
  found 
  it 
  of 
  much 
  service 
  on 
  account 
  of 
  the 
  old 
  difficulty 
  

   of 
  the 
  pigment 
  cells, 
  which 
  are 
  stained 
  so 
  deeply 
  as 
  to 
  

   obscure 
  any 
  other 
  structures 
  with 
  which 
  they 
  are 
  in 
  

   contact. 
  

  

  Methylene 
  blue, 
  Ranvier's 
  lemon 
  juice 
  method, 
  and 
  other 
  

   nerve 
  processes 
  have 
  been 
  tried, 
  but 
  without 
  any 
  marked 
  

   success. 
  

  

  A 
  method 
  which 
  promises 
  good 
  results 
  in 
  the 
  differen- 
  

   tiation 
  of 
  nerve 
  tissue 
  seems 
  to 
  be 
  the 
  double 
  impregnation 
  

   of 
  silver 
  chromate 
  already 
  referred 
  to. 
  Like 
  most 
  of 
  these 
  

   processes 
  it 
  is 
  exceedingly 
  capricious, 
  and 
  too 
  much 
  must 
  

   not 
  be 
  expected 
  of 
  it. 
  Sometimes 
  nerves 
  in 
  one 
  part 
  of 
  a 
  

   section 
  will 
  be 
  differentiated, 
  whilst 
  in 
  others 
  they 
  remain 
  

   unstained. 
  Moreover, 
  the 
  material 
  so 
  prepared 
  will 
  rarely 
  

   stand 
  the 
  usual 
  embedding 
  processes, 
  and 
  I 
  find 
  the 
  most 
  

   likely 
  method 
  of 
  seeing 
  the 
  structures 
  required 
  is 
  to 
  tease 
  

   out 
  on 
  a 
  sUde 
  small 
  portions 
  of 
  the 
  tissue 
  and 
  examine 
  

   them 
  as 
  non-permanent 
  preparations. 
  The 
  material 
  is 
  

   placed 
  in 
  a 
  2 
  % 
  solution 
  of 
  potassium 
  bichromate 
  to 
  which 
  

   a 
  very 
  little 
  formol 
  has 
  been 
  added, 
  and 
  the 
  tube 
  exhausted 
  

   of 
  air. 
  The 
  material 
  remains 
  in 
  this 
  solution 
  for 
  about 
  

   three 
  days, 
  when 
  it 
  is 
  placed 
  in 
  1 
  % 
  silver 
  nitrate 
  for 
  two 
  

   days, 
  then 
  returned 
  to 
  the 
  bichromate 
  solution 
  (freshly 
  

   prepared) 
  for 
  two 
  days, 
  and 
  finally 
  put 
  back 
  into 
  silver 
  

   nitrate 
  for 
  two 
  days 
  or 
  more. 
  It 
  can 
  then 
  be 
  washed 
  in 
  

   90 
  % 
  alcohol 
  and 
  examined. 
  

  

  For 
  section 
  -cutting 
  I 
  have 
  used 
  both 
  paraffin 
  and 
  paraffin- 
  

   celloidin. 
  If 
  chitinous 
  parts 
  are 
  not 
  required, 
  cornea, 
  etc., 
  

   can 
  be 
  removed 
  after 
  fixation 
  and 
  only 
  the 
  soft 
  parts 
  left. 
  

   Paraffin 
  sections 
  can 
  then 
  easily 
  be 
  made. 
  For 
  sections 
  

   including 
  the 
  chitin 
  I 
  have 
  found 
  the 
  following 
  process 
  

   the 
  most 
  satisfactory. 
  

  

  Fixed 
  and 
  dehydrated 
  material 
  is 
  placed 
  for 
  two 
  or 
  

   three 
  days 
  in 
  a 
  solution 
  of 
  celloidin 
  in 
  clove 
  oil.* 
  Then 
  

  

  * 
  Celloidin 
  dissolves 
  in 
  clove 
  oil 
  only 
  very 
  slowly. 
  Many 
  weeks 
  

   may 
  be 
  required 
  for 
  the 
  solution 
  to 
  become 
  saturated. 
  

  

  