﻿360 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  2 
  9 
  

  

  forced 
  to 
  conclude 
  that 
  the 
  minute 
  amounts 
  of 
  natural 
  radiation 
  

   present 
  almost 
  everywhere 
  in 
  nature, 
  most 
  of 
  it 
  of 
  terrestrial 
  origin, 
  

   due 
  to 
  the 
  radium 
  and 
  other 
  radioactive 
  substances 
  on 
  earth 
  (some 
  

   inside 
  the 
  organism), 
  and 
  a 
  smaller 
  part 
  of 
  it 
  of 
  cosmic 
  origin, 
  appar- 
  

   ently 
  derived 
  from 
  the 
  diffuse 
  and 
  distant 
  factories 
  of 
  matter 
  — 
  all 
  this 
  

   natural 
  radiation 
  must 
  be 
  producing 
  some 
  mutations 
  in 
  the 
  living 
  

   things 
  on 
  the 
  earth. 
  These 
  mutations 
  must 
  be 
  very 
  scattered 
  and 
  

   very 
  infrequent 
  in 
  proportion 
  to 
  the 
  total 
  nonmutated 
  population, 
  

   just 
  because 
  the 
  amount 
  of 
  natural 
  short 
  wave 
  length 
  radiation 
  is 
  

   very 
  small 
  in 
  any 
  given 
  case, 
  but, 
  considering 
  the 
  extent 
  of 
  the 
  earth 
  

   and 
  the 
  multiplicity 
  of 
  living 
  things, 
  the 
  total 
  number 
  of 
  mutations 
  

   so 
  produced 
  per 
  year 
  must 
  be 
  very 
  considerable. 
  It 
  can, 
  therefore, 
  

   scarcely 
  be 
  denied 
  that 
  in 
  this 
  factor 
  we 
  have 
  found 
  at 
  least 
  one 
  of 
  

   the 
  natural 
  causes 
  of 
  mutation, 
  and 
  hence 
  of 
  evolution. 
  

  

  How 
  important 
  is 
  this 
  cause 
  relatively? 
  Is 
  it 
  the 
  sole 
  cause 
  of 
  

   evolution? 
  We 
  do 
  not 
  yet 
  know. 
  Returning 
  to 
  the 
  investigation 
  

   of 
  the 
  possible 
  effectiveness 
  of 
  poisons 
  and 
  influences 
  other 
  than 
  X 
  

   rays 
  I 
  have 
  during 
  the 
  past 
  two 
  5^ears 
  tried 
  out 
  a 
  number 
  of 
  drastic 
  

   treatments, 
  using 
  a 
  refined 
  genetic 
  technique 
  similar 
  to 
  that 
  in 
  the 
  X- 
  

   ray 
  experiments, 
  which 
  would 
  have 
  allowed 
  of 
  the 
  detection 
  of 
  lethal? 
  

   and 
  other 
  mutations 
  with 
  far 
  greater 
  ease, 
  and 
  therefore 
  in 
  greatei 
  

   abundance, 
  than 
  in 
  the 
  inconclusive 
  experiments 
  of 
  the 
  past. 
  In- 
  

   cluded 
  among 
  the 
  treatments 
  were 
  heavy 
  doses 
  of 
  manganese 
  and 
  of 
  

   lead 
  salts, 
  which 
  had 
  been 
  claimed 
  by 
  J. 
  W. 
  H. 
  Harrison 
  (on 
  the 
  

   basis 
  of 
  what 
  appeared 
  to 
  me 
  genetically 
  unconvincing 
  data) 
  to 
  pro- 
  

   duce 
  visible 
  mutations 
  in 
  butterflies. 
  There 
  was 
  also 
  included 
  a 
  repe- 
  

   tition 
  of 
  the 
  experiments 
  recently 
  reported 
  by 
  Morgan, 
  Sturtevant, 
  

   and 
  Bridges, 
  who 
  suspected 
  that 
  they 
  had 
  been 
  able 
  to 
  cause 
  visible 
  

   mutations 
  in 
  red-eyed 
  flies 
  by 
  injuring 
  their 
  eyes 
  with 
  a 
  hot 
  needle, 
  an 
  

   operation 
  which 
  was 
  followed 
  by 
  a 
  release 
  of 
  the 
  optic 
  pigment 
  and 
  its 
  

   distribution 
  throughout 
  the 
  body.^ 
  Our 
  trials 
  of 
  all 
  these 
  and 
  other 
  

   agencies 
  have 
  given 
  negative 
  results, 
  and 
  it 
  is 
  becoming 
  a 
  question 
  

   where 
  to 
  stop. 
  

  

  On 
  the 
  other 
  hand, 
  it 
  is 
  true 
  that 
  other 
  conditions, 
  internal 
  and 
  per- 
  

   haps 
  also 
  external, 
  accompanying 
  the 
  X-ray 
  treatment, 
  may 
  somehow 
  

   affect 
  the 
  sensitivity 
  of 
  the 
  cells 
  to 
  that 
  treatment. 
  Thus 
  Stadler 
  

   finds 
  that 
  the 
  sprouting 
  cells 
  of 
  seedlings 
  have 
  mutations 
  produced 
  in 
  

   them 
  in 
  much 
  greater 
  abuu 
  dance 
  by 
  a 
  given 
  dose 
  of 
  X 
  rays, 
  than 
  the 
  

   dormant 
  cells 
  of 
  seeds 
  ci 
  > 
  though 
  some 
  mutations 
  are 
  produced 
  in 
  both. 
  

   On 
  the 
  other 
  hand, 
  both 
  Hanson 
  and 
  Harris, 
  working 
  independently, 
  

   find 
  that 
  the 
  genes 
  of 
  growing 
  immature 
  germ 
  cells 
  are 
  far 
  less 
  sensitive 
  

   to 
  the 
  mutating 
  effect 
  of 
  radium 
  or 
  X 
  rays 
  than 
  are 
  the 
  dormant 
  

  

  * 
  They 
  announce 
  that 
  they 
  have 
  recently 
  been 
  elaborating 
  upon 
  this 
  work 
  by 
  similar 
  tests 
  on 
  flies 
  with 
  

   other 
  eye 
  colors, 
  and 
  by 
  artificial 
  injection 
  of 
  substances 
  derived 
  from 
  the 
  eyes. 
  Guyer, 
  who 
  originated 
  

   these 
  methods 
  in 
  experiments 
  with 
  rabbits, 
  had 
  claimed 
  positive 
  results 
  from 
  them 
  in 
  his 
  material. 
  

  

  