﻿EFFECTS 
  OF 
  SOLAR 
  RADIATION 
  — 
  O'BRIEN 
  131 
  

  

  As 
  early 
  as 
  1877 
  Downes 
  and 
  Blunt 
  investigated 
  the 
  destruction 
  of 
  

   putrefactive 
  bacteria 
  by 
  sunlight 
  and 
  made 
  rough 
  measurements 
  of 
  

   the 
  relative 
  action 
  of 
  different 
  colors. 
  There 
  followed 
  many 
  investi- 
  

   gations 
  of 
  the 
  effect 
  of 
  ultraviolet 
  light 
  on 
  bacteria, 
  but 
  the 
  spectral- 
  

   response 
  curve 
  for 
  this 
  reaction 
  was 
  not 
  determined 
  for 
  more 
  than 
  50 
  

   years. 
  It 
  was 
  measured 
  by 
  H. 
  W. 
  Lyall 
  and 
  myself 
  in 
  1926 
  and 
  inde- 
  

   pendently 
  by 
  Sonne 
  in 
  1927. 
  We 
  had 
  expected 
  the 
  spectral-response 
  

   curve 
  to 
  be 
  quite 
  different 
  for 
  different 
  bacteria, 
  but 
  to 
  our 
  surprise 
  

   eight 
  pathogenic 
  and 
  two 
  saprophytic 
  organisms 
  showed 
  surprising 
  

   similarity 
  in 
  spectral 
  response, 
  although 
  those 
  selected 
  included 
  cocci, 
  

   Gram-negative 
  baccili, 
  and 
  two 
  acid-fast 
  strains. 
  Our 
  most 
  complete 
  

  

  DEC* 
  

  

  Figube 
  24. 
  — 
  Seasonal 
  variation 
  in 
  solar 
  erythema 
  effect. 
  (3.0 
  mm. 
  zenith 
  ozone, 
  

  

  43° 
  N. 
  latitude.) 
  

  

  work 
  was 
  done 
  with 
  a 
  strain 
  of 
  Staphylococcus 
  aureus. 
  The 
  spectral 
  

   response 
  of 
  this 
  organism 
  is 
  shown 
  in 
  figure 
  25. 
  It 
  is 
  interesting 
  to 
  

   note 
  that 
  Sonne's 
  measurements 
  on 
  the 
  colon 
  bacillus 
  agree 
  almost 
  

   perfectly 
  with 
  this 
  curve, 
  although 
  the 
  characteristics 
  of 
  the 
  colon 
  

   bacillus 
  are 
  different 
  in 
  every 
  respect 
  from 
  those 
  of 
  Staphylococcus 
  

   aureus. 
  More 
  recently 
  similar 
  measurements 
  have 
  been 
  made 
  by 
  

   Gates, 
  with 
  good 
  agreement 
  over 
  part 
  but 
  not 
  all 
  of 
  the 
  spectral 
  range. 
  

   We 
  may 
  calculate 
  the 
  seasonal 
  variation 
  in 
  the 
  bactericidal 
  effect 
  

   of 
  sunlight 
  by 
  following 
  the 
  same 
  procedure 
  already 
  applied 
  to 
  the 
  

   antirachitic 
  and 
  erythema 
  reactions. 
  This 
  has 
  been 
  carried 
  out 
  to 
  

   form 
  the 
  product 
  curves 
  of 
  figure 
  26, 
  for 
  the 
  condition 
  of 
  3.0 
  milli- 
  

   meters 
  of 
  ozone 
  in 
  the 
  zenith 
  atmosphere. 
  The 
  integrals 
  of 
  these 
  

  

  