﻿Dr. 
  H. 
  Eltringham 
  on 
  Butterfly 
  Vision. 
  31 
  

  

  transfer 
  the 
  material 
  to 
  a 
  weak 
  solution 
  of 
  celloidin 
  in 
  

   ether 
  and 
  alcohol, 
  and 
  concentrate 
  to 
  a 
  syrup 
  at 
  about 
  

   40° 
  C. 
  Pour 
  into 
  a 
  mould 
  and 
  harden 
  in 
  chloroform 
  vapour 
  

   in 
  the 
  usual 
  way, 
  and 
  then 
  transfer 
  to 
  a 
  saturated 
  solution 
  

   of 
  paraffin 
  in 
  chloroform 
  for 
  twenty-four 
  hours. 
  Then 
  

   place 
  the 
  block 
  in 
  melted 
  paraffin 
  having 
  a 
  melting 
  point 
  

   of 
  about 
  55° 
  C. 
  and 
  exhaust 
  with 
  a 
  water 
  air-pump, 
  finally 
  

   embedding 
  in 
  fresh 
  melted 
  paraffin. 
  

  

  This 
  combination 
  of 
  clove 
  -oil 
  celloidin 
  saturation 
  with 
  

   double 
  embedding 
  was 
  suggested 
  by 
  Dr. 
  C. 
  J. 
  Martin 
  of 
  

   the 
  Lister 
  Institute. 
  In 
  my 
  experience 
  it 
  is 
  superior 
  

   to 
  the 
  much 
  -vaunted 
  spirit-soap 
  treatment. 
  The 
  alleged 
  

   chitin-softening 
  action 
  of 
  spirit-soap 
  seems 
  to 
  me 
  to 
  be 
  

   much 
  over- 
  rated. 
  

  

  Nearly 
  all 
  my 
  sections 
  were 
  cut 
  with 
  a 
  Cambridge 
  Rock- 
  

   ing 
  Microtome, 
  which, 
  except 
  for 
  pure 
  celloidin 
  sections, 
  

   is 
  quite 
  as 
  efficient 
  as 
  the 
  more 
  complicated 
  and 
  costly 
  

   instruments. 
  

  

  Can 
  Butterflies 
  distinguish 
  Colours? 
  

  

  Before 
  investigating 
  this 
  question 
  and 
  considering 
  such 
  

   experiments 
  as 
  may 
  be 
  regarded 
  as 
  throwing 
  some 
  light 
  

   on 
  the 
  subject, 
  it 
  will 
  be 
  as 
  well 
  to 
  make 
  clear 
  the 
  mean- 
  

   ing 
  of 
  the 
  question 
  and 
  the 
  necessary 
  limitations 
  of 
  any 
  

   answer 
  thereto. 
  We 
  know 
  that 
  hght 
  consists 
  of 
  vibrations 
  

   or 
  waves, 
  and 
  since 
  we 
  cannot 
  imagine 
  waves 
  in 
  nothing, 
  

   and 
  since 
  hght 
  reaches 
  us 
  from 
  the 
  stars 
  across 
  ilhmitable 
  

   tracts 
  of 
  empty 
  space, 
  we 
  suppose 
  the 
  existence 
  of 
  an 
  

   invisible, 
  intangible, 
  perfectly 
  elastic 
  medium 
  called 
  the 
  

   aether, 
  which 
  is 
  considered 
  to 
  permeate 
  the 
  universe 
  and 
  

   all 
  material 
  substances 
  contained 
  therein. 
  The 
  vibrations 
  

   set 
  up 
  in 
  this 
  medium 
  by 
  a 
  source 
  of 
  light 
  are 
  of 
  differing 
  

   wave 
  lengths 
  and 
  wave 
  frequencies, 
  and 
  our 
  own 
  visual 
  

   organs 
  record 
  different 
  sensations 
  according 
  to 
  the 
  fre- 
  

   quencies 
  of 
  the 
  waves 
  which 
  fall 
  upon 
  our 
  eyes. 
  The 
  hght 
  

   we 
  receive 
  on 
  our 
  own 
  retina 
  may 
  come 
  direct 
  from 
  the 
  

   source 
  of 
  light, 
  or 
  more 
  commonly 
  may 
  be 
  reflected 
  from 
  

   the 
  surface 
  of 
  some 
  substance 
  upon 
  which 
  the 
  direct 
  light 
  

   is 
  falling. 
  If 
  the 
  light 
  we 
  receive 
  contains 
  a 
  normal 
  

   admixture 
  of 
  all 
  the 
  rays 
  of 
  differing 
  length 
  and 
  frequency 
  

   we 
  experience 
  a 
  sensation 
  which 
  we 
  call 
  " 
  white." 
  It 
  is 
  

   possible 
  to 
  separate 
  the 
  component 
  rays 
  of 
  white 
  hglit 
  

   by 
  passing 
  them 
  through 
  a 
  prism, 
  as 
  in 
  the 
  well-known 
  

  

  