﻿126 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  The 
  phenomenon 
  of 
  sunburn 
  is 
  probably 
  of 
  less 
  physiological 
  im- 
  

   portance 
  than 
  the 
  antirachitic 
  effect 
  of 
  sunlight, 
  but 
  it 
  has 
  seemed 
  

   worth 
  while 
  to 
  calculate 
  the 
  relative 
  erythema 
  production 
  by 
  sunlight 
  

   for 
  one 
  latitude, 
  43°, 
  and 
  for 
  one 
  ozone 
  quantity, 
  3.0 
  millimeters 
  S. 
  T. 
  

   P. 
  Using 
  the 
  data 
  for 
  erythema 
  reaction 
  per 
  unit 
  energy 
  as 
  a 
  func- 
  

   tion 
  of 
  wave 
  length 
  shown 
  in 
  figure 
  2, 
  the 
  series 
  of 
  product 
  curves 
  

   shown 
  in 
  figure 
  22 
  have 
  been 
  calculated 
  by 
  the 
  same 
  procedure 
  fol- 
  

   lowed 
  in 
  obtaining 
  the 
  curves 
  of 
  figures 
  9 
  and 
  10. 
  The 
  integrals 
  of 
  

   these 
  curves 
  as 
  represented 
  by 
  the 
  area 
  under 
  each 
  are 
  shown 
  in 
  figure 
  

   23 
  and 
  are 
  analogous 
  to 
  the 
  results 
  plotted 
  in 
  figure 
  11. 
  Finally, 
  

   in 
  figure 
  24 
  are 
  shown 
  the 
  results 
  for 
  erythema 
  reaction 
  under 
  sun- 
  

  

  TIME 
  OF 
  DM 
  

  

  Figube 
  15. 
  — 
  Hourly 
  variation 
  of 
  solar 
  antirachitic 
  effect. 
  (2.0 
  mm. 
  zenith 
  ozone, 
  

  

  38° 
  N. 
  latitude.) 
  

  

  light 
  at 
  noon 
  on 
  clear 
  days 
  as 
  a 
  function 
  of 
  time 
  of 
  year 
  for 
  latitude 
  

   43° 
  and 
  3.0 
  millimeters 
  of 
  ozone 
  in 
  the 
  zenith 
  atmosphere. 
  The 
  ex- 
  

   posure 
  to 
  sunlight 
  necessary 
  to 
  produce 
  an 
  erythema 
  varies 
  greatly 
  

   among 
  individuals 
  and 
  is 
  dependent 
  upon 
  the 
  condition 
  of 
  the 
  skin. 
  

   The 
  skin 
  of 
  a 
  sensitive 
  individual 
  not 
  previously 
  exposed 
  to 
  ultra- 
  

   violet 
  radiation 
  will 
  show 
  an 
  erythema 
  reaction 
  if 
  exposed 
  for 
  about 
  

   15 
  minutes 
  to 
  zenith 
  sunlight 
  through 
  3.0 
  millimeters 
  of 
  ozone. 
  

  

  In 
  contrast 
  with 
  the 
  effects 
  just 
  discussed, 
  the 
  destruction 
  of 
  bac- 
  

   teria 
  by 
  ultraviolet 
  light 
  is 
  a 
  typical 
  example 
  of 
  the 
  influence 
  of 
  

   radiation 
  upon 
  micro-organisms. 
  Also 
  it 
  is 
  probable 
  that 
  its 
  impor- 
  

   tance 
  to 
  the 
  human 
  race 
  is 
  as 
  great 
  as 
  any 
  of 
  the 
  reactions 
  mentioned 
  

   above, 
  for 
  by 
  this 
  means 
  sunlight 
  keeps 
  bacterial 
  growth 
  in 
  check. 
  

   Because 
  of 
  the 
  small 
  size 
  of 
  the 
  individual 
  bacterium 
  most 
  of 
  the 
  ultra- 
  

   violet 
  radiation 
  incident 
  upon 
  the 
  bacterial 
  cell 
  passes 
  on 
  through, 
  

  

  