﻿EFFECTS 
  OF 
  SOLAR 
  RADIATION 
  — 
  O'BRIEN 
  133 
  

  

  curves 
  (i. 
  e., 
  the 
  areas 
  under 
  each 
  curve) 
  are 
  plotted 
  in 
  figure 
  27, 
  

   showing 
  the 
  bactericidal 
  effect 
  of 
  sunlight 
  as 
  a 
  function 
  of 
  air 
  mass 
  

   for 
  3.0 
  millimeters 
  of 
  ozone 
  in 
  a 
  zenith 
  atmosphere. 
  In 
  figure 
  28 
  is 
  

   plotted 
  the 
  bactericidal 
  effect 
  as 
  a 
  function 
  of 
  time 
  of 
  year 
  for 
  clear 
  

   days 
  at 
  noon, 
  43° 
  N. 
  latitude. 
  Although 
  the 
  general 
  trend 
  of 
  this 
  

   curve 
  with 
  time 
  of 
  year 
  is 
  similar 
  to 
  the 
  curve 
  for 
  antirachitic 
  and 
  

   erythema 
  effects, 
  it 
  will 
  be 
  noted 
  that 
  the 
  summer-to-winter 
  differ- 
  

   ence 
  is 
  even 
  greater. 
  Because 
  of 
  this 
  the 
  effective 
  bactericidal 
  action 
  

   of 
  sunlight 
  is 
  even 
  more 
  dependent 
  upon 
  short 
  air 
  path 
  (sun 
  near 
  

  

  Figtjbe 
  27. 
  — 
  Variation 
  of 
  solar 
  bactericidal 
  effect 
  with 
  air 
  mass. 
  (3.0 
  mm. 
  ozone 
  

  

  in 
  zenith 
  atmosphere.) 
  

  

  zenith) 
  than 
  are 
  the 
  antirachitic 
  and 
  erythemal 
  reactions. 
  Thus 
  the 
  

   effects 
  of 
  latitude, 
  time 
  of 
  year, 
  and 
  time 
  of 
  day 
  are 
  all 
  more 
  

   pronounced. 
  

  

  In 
  spite 
  of 
  the 
  similarity 
  in 
  the 
  spectral 
  sensitivity 
  of 
  different 
  bac- 
  

   teria 
  to 
  ultraviolet 
  light, 
  there 
  is 
  a 
  considerable 
  difference 
  in 
  the 
  ab- 
  

   solute 
  exposure 
  necessary 
  to 
  destroy 
  different 
  strains. 
  Acid-fast 
  or- 
  

   ganisms, 
  such 
  as 
  the 
  tubercle 
  bacillus, 
  are 
  relatively 
  resistant 
  to 
  ultra- 
  

   violet 
  light 
  and 
  require 
  for 
  their 
  destruction 
  an 
  exposure 
  of 
  about 
  14 
  

   minutes 
  to 
  zenith 
  sunlight 
  through 
  3.0 
  millimeters 
  of 
  ozone. 
  Certain 
  

   Gram-negative 
  organisms, 
  such 
  as 
  the 
  colon 
  bacillus 
  and 
  particularly 
  

   Baccillus 
  paratyphosus 
  B, 
  require 
  an 
  exposure 
  of 
  only 
  about 
  2 
  min- 
  

   utes 
  to 
  sunlight 
  for 
  complete 
  destruction. 
  Most 
  pathogenic 
  bacteria 
  

   appear 
  to 
  lie 
  between 
  these 
  two 
  extremes 
  as 
  regard 
  sensitivity 
  to 
  

   ultraviolet 
  light. 
  From 
  this 
  the 
  scale 
  can 
  be 
  set 
  for 
  figures 
  27 
  and 
  28. 
  

  

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