﻿EFFECTS 
  OF 
  SOLAR 
  RADIATION 
  — 
  O'BRIEN 
  113 
  

  

  there 
  appear 
  to 
  be 
  no 
  other 
  specific 
  effects 
  of 
  sunlight 
  upon 
  any 
  por- 
  

   tion 
  of 
  the 
  animal 
  organism 
  until 
  the 
  ultraviolet 
  limit 
  of 
  the 
  sun's 
  

   spectrum 
  is 
  reached. 
  Effects 
  of 
  visible 
  light 
  upon 
  the 
  eye 
  are, 
  of 
  

   course, 
  most 
  important 
  and 
  profound, 
  but 
  except 
  under 
  destructively 
  

   intense 
  illumination, 
  the 
  response 
  of 
  the 
  eye 
  appears 
  to 
  be 
  limited 
  

   to 
  providing 
  us 
  with 
  a 
  sensory 
  contact 
  with 
  the 
  external 
  world. 
  The 
  

   subject 
  of 
  vision 
  belongs 
  properly 
  in 
  the 
  field 
  of 
  sensory 
  physiology 
  

   and 
  psychology 
  and 
  is 
  not 
  included 
  in 
  the 
  types 
  of 
  biological 
  reaction 
  

   I 
  am 
  discussing 
  tonight; 
  so, 
  for 
  lack 
  of 
  time, 
  and 
  with 
  some 
  reluc- 
  

   tance, 
  I 
  shall 
  omit 
  it 
  entirely. 
  

  

  Most 
  of 
  you, 
  I 
  am 
  sure, 
  have 
  experienced 
  sunburn, 
  or 
  erythema, 
  

   produced 
  by 
  light, 
  but 
  have 
  you 
  considered 
  how 
  it 
  comes 
  about? 
  In 
  

  

  3200 
  

  

  Figure 
  2. 
  — 
  Erythema 
  sensitivity 
  of 
  human 
  skin. 
  

  

  spite 
  of 
  its 
  name, 
  sunburn 
  is 
  not 
  a 
  heat 
  reaction, 
  but 
  a 
  photochemical 
  

   reaction, 
  produced 
  without 
  heat 
  by 
  ultraviolet 
  light. 
  Moreover, 
  it 
  is 
  

   not 
  produced 
  by 
  all 
  the 
  ultraviolet 
  spectrum, 
  but 
  only 
  by 
  a 
  very 
  nar- 
  

   row 
  region 
  at 
  the 
  extreme 
  ultraviolet 
  limit 
  of 
  the 
  sun's 
  spectrum 
  

   confined 
  to 
  wave 
  lengths 
  less 
  than 
  about 
  3150 
  angstrom 
  units. 
  This 
  

   reaction 
  appears 
  to 
  be 
  a 
  type 
  of 
  photo-oxidation, 
  produced 
  with 
  the 
  

   aid 
  of 
  certain 
  enzymes 
  present 
  in 
  normal 
  skin. 
  Hausser 
  and 
  Vahle, 
  

   and 
  later 
  Hausser, 
  determined 
  the 
  spectral 
  sensitivity 
  of 
  this 
  re- 
  

   action, 
  obtaining 
  a 
  reaction 
  curve 
  showing 
  two 
  maxima 
  and 
  ap- 
  

   proaching 
  zero 
  for 
  wave 
  lengths 
  longer 
  than 
  about 
  3150 
  angstroms. 
  

   This 
  is 
  shown 
  in 
  figure 
  2. 
  These 
  results 
  have 
  been 
  confirmed 
  by 
  

   Luckiesh, 
  Holliday, 
  and 
  Taylor. 
  The 
  significance 
  of 
  erythema 
  and 
  

  

  