﻿352 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  192 
  9 
  

  

  must 
  be 
  regarded 
  as 
  the 
  results 
  of 
  ultramicroscopic 
  accidents 
  — 
  events 
  

   too 
  far 
  removed 
  in 
  fineness 
  to 
  be 
  readily 
  susceptible 
  of 
  any 
  exact 
  

   control 
  on 
  our 
  part. 
  In 
  other 
  words, 
  an 
  appeal 
  was 
  made 
  to 
  the 
  

   newly 
  found 
  world 
  of 
  the 
  little 
  which 
  the 
  old-line 
  biologist 
  and 
  phi- 
  

   losopher 
  do 
  not 
  always 
  take 
  sufficiently 
  into 
  consideration. 
  

  

  The 
  genes 
  are 
  not 
  only 
  protected 
  by 
  a 
  cell 
  membrane 
  but 
  by 
  a 
  

   nuclear 
  membrane 
  inside 
  of 
  that, 
  and 
  possibly 
  again 
  by 
  a 
  chromosomal 
  

   envelope 
  of 
  some 
  Idnd; 
  they 
  may 
  be 
  well 
  shielded, 
  therefore, 
  from 
  the 
  

   reach 
  of 
  many 
  poisonous 
  substances 
  and 
  unusual 
  products 
  of 
  metabo- 
  

   lism. 
  They 
  can 
  not, 
  however, 
  escape 
  the 
  interplay 
  of 
  the 
  helter- 
  

   skelter 
  molecular, 
  atomic, 
  and 
  electronic 
  motions 
  that 
  are 
  continually 
  

   taking 
  place 
  both 
  within 
  and 
  around 
  them, 
  on 
  the 
  part 
  of 
  the 
  substances 
  

   of 
  which 
  they 
  and 
  their 
  neighbor 
  molecules 
  are 
  naturally 
  composed. 
  

   Nor 
  can 
  they 
  escape 
  the 
  buffeting 
  action 
  of 
  the 
  electromagnetic 
  

   stresses 
  and 
  strains 
  occurring 
  through 
  space 
  in 
  the 
  field 
  in 
  which 
  thej^ 
  

   lie 
  immersed. 
  These 
  various 
  exchanges 
  of 
  energy 
  are 
  not, 
  it 
  is 
  evident, 
  

   ordinarily 
  consequential 
  enough, 
  or 
  the 
  energy 
  is 
  not 
  directed 
  in 
  

   sufficiently 
  telling 
  ways, 
  so 
  to 
  distort 
  a 
  gene 
  as 
  to 
  change 
  its 
  composi- 
  

   tion 
  permanently. 
  Occasionally, 
  however, 
  such 
  a 
  change 
  does 
  occur, 
  

   and 
  subsequent 
  generations 
  tell 
  the 
  tale. 
  

  

  X 
  RAYS 
  A 
  CAUSE 
  OF 
  MUTATIONS 
  

  

  If 
  this 
  general 
  conception 
  of 
  mutation 
  is 
  valid 
  we 
  must 
  regard 
  it 
  as 
  

   merely 
  a 
  kind 
  of 
  placing 
  of 
  the 
  problem; 
  we 
  should 
  not 
  yet 
  know 
  just 
  

   which 
  were 
  ordinarily 
  the 
  critical 
  processes 
  concerned, 
  still 
  less 
  the 
  

   exact 
  steps 
  involved. 
  The 
  conception 
  carries 
  with 
  it, 
  however, 
  

   suggestions 
  for 
  further 
  experimental 
  investigation. 
  For 
  among 
  the 
  

   agents 
  of 
  an 
  ultramicroscopically 
  random 
  character, 
  that 
  can 
  strike 
  

   willy-nilly 
  through 
  living 
  things, 
  causing 
  drastic 
  atomic 
  changes 
  here 
  

   and 
  passing 
  everything 
  by 
  unaltered 
  there 
  — 
  not 
  a 
  ten 
  thousandth 
  

   of 
  a 
  millimeter 
  away, 
  there 
  stand 
  preeminently 
  the 
  X 
  or 
  7 
  ray 
  and 
  its 
  

   accomplice, 
  the 
  speeding 
  electron. 
  

  

  There 
  is 
  nothing 
  in 
  protoplasm 
  which 
  can 
  effectually 
  stop 
  the 
  pas- 
  

   sage 
  of 
  X 
  rays 
  or 
  the 
  related 
  waves 
  of 
  shorter 
  wave 
  length 
  — 
  gamma 
  

   and 
  cosmic 
  rays. 
  For 
  the 
  most 
  part, 
  in 
  a 
  cell, 
  the 
  rays 
  will 
  pass 
  

   through; 
  but 
  at 
  isolated, 
  unpredictable 
  spots, 
  depending 
  upon 
  

   unknown 
  "chance" 
  details 
  of 
  energy 
  configurations, 
  a 
  definite 
  

   portion, 
  a 
  "quantum" 
  of 
  the 
  rays 
  will 
  be 
  held 
  up, 
  and 
  the 
  energy 
  thus 
  

   absorbed 
  will 
  issue 
  forth 
  in 
  a 
  hurthng 
  electron, 
  shot 
  out 
  of 
  the 
  atom 
  

   that 
  stood 
  in 
  the 
  way 
  of 
  the 
  radiation. 
  The 
  atom 
  will 
  be 
  changed 
  

   thereby, 
  and 
  hence 
  the 
  molecule 
  in 
  which 
  it 
  lies 
  may 
  undergo 
  a 
  change 
  

   in 
  its 
  chemical 
  composition. 
  But 
  for 
  every 
  atom 
  thus 
  directly 
  changed 
  

   there 
  are 
  hundreds 
  of 
  other 
  atoms 
  changed 
  indu-ectly. 
  For 
  the 
  

   electron, 
  shot 
  out 
  like 
  a 
  bullet 
  (except 
  far 
  faster), 
  tears 
  its 
  path 
  through 
  

   hundreds 
  of 
  atoms 
  that 
  happen 
  to 
  lie 
  in 
  its 
  way, 
  leaving 
  in 
  its 
  wake 
  a 
  

  

  