﻿602 
  GEORGE 
  WAGNER. 
  

  

  Jeuuiugs 
  (1. 
  c.) 
  pp. 
  49-51) 
  discusses 
  at 
  length 
  tlie 
  possible 
  

   explaiiatiou 
  for 
  the 
  failure 
  ou 
  part 
  of 
  aii 
  organism 
  to 
  react 
  to 
  

   a 
  stimulus 
  to 
  Avhich 
  at 
  first 
  it 
  responds 
  very 
  readily. 
  The 
  

   three 
  possibilities 
  he 
  mentions 
  are 
  motor 
  fatigue^ 
  sensory 
  

   fatigue^ 
  and 
  a 
  third 
  unknown 
  element. 
  The 
  facts 
  concerning 
  

   Hydra 
  that 
  bear 
  on 
  this 
  matter 
  fully 
  support 
  Jennings' 
  con- 
  

   tention. 
  Motor 
  fatigue 
  is 
  entirely 
  out 
  of 
  the 
  question, 
  for 
  I 
  

   have 
  been 
  able, 
  under 
  proper 
  conditions, 
  to 
  keep 
  Hydra 
  con- 
  

   tracting 
  continuously 
  for 
  as 
  long 
  as 
  three 
  hours, 
  at 
  the 
  end 
  of 
  

   which 
  time 
  it 
  responded 
  as 
  readily 
  as 
  at 
  the 
  beginning. 
  

   Furthermore, 
  we 
  have 
  seen 
  that 
  after 
  long 
  repeated 
  stimula- 
  

   tion 
  at 
  such 
  frequent 
  intervals 
  as 
  to 
  bar 
  any 
  possibility 
  of 
  

   recovery 
  from 
  fatigue. 
  Hydra 
  finally 
  undertakes 
  the 
  very 
  

   complicated 
  " 
  escape 
  " 
  movement. 
  This, 
  in 
  itself, 
  involves 
  a 
  

   large 
  amount 
  of 
  work, 
  and 
  makes 
  explanation 
  by 
  motor 
  fatigue 
  

   impossible. 
  

  

  Further, 
  this 
  last-mentioned 
  "^^ 
  escape 
  " 
  movement 
  proves, 
  

   with 
  equal 
  force, 
  that 
  the 
  stimulus 
  is 
  still 
  perceived, 
  otherwise 
  

   there 
  could 
  be 
  no 
  reaction. 
  This 
  being 
  the 
  case, 
  the 
  explana- 
  

   tion 
  by 
  sensory 
  fatigue 
  is 
  clearly 
  inadmissible. 
  There 
  remains 
  

   only 
  the 
  third 
  possibility. 
  We 
  may 
  suppose 
  that 
  the 
  stimulus 
  

   which 
  causes 
  a 
  contraction 
  at 
  the 
  same 
  time 
  affects 
  the 
  physio- 
  

   logical 
  condition 
  of 
  the 
  organism 
  in 
  such 
  a 
  way 
  that 
  the 
  limen 
  

   for 
  that 
  particular 
  character 
  of 
  stimulation 
  is 
  raised. 
  If 
  part 
  

   of 
  the 
  energy 
  involved 
  in 
  the 
  stimulus 
  comes 
  to 
  act 
  on 
  the 
  

   chemical 
  constituents 
  of 
  the 
  organism 
  this 
  may 
  well 
  cause 
  a 
  

   change 
  in 
  the 
  character 
  of 
  these 
  constituents. 
  Irritability 
  

   must 
  depend 
  largely 
  on 
  the 
  chemical 
  character 
  of 
  these 
  con- 
  

   stituents 
  ; 
  this, 
  it 
  seems 
  to 
  me, 
  is 
  well 
  shown 
  by 
  the 
  action 
  of 
  

   narcotics 
  and 
  anassthetics. 
  Therefore, 
  a 
  chemical 
  change 
  in 
  

   body 
  constituents 
  would 
  necessarily 
  involve 
  a 
  change 
  in 
  irri- 
  

   tability, 
  and 
  so 
  a 
  change 
  in 
  the 
  readiness 
  of 
  response 
  to 
  

   stimulation. 
  These 
  considerations 
  may 
  very 
  well 
  explain 
  the 
  

   lack 
  of 
  response 
  after 
  repeated 
  stimulations. 
  

  

  The 
  return 
  of 
  the 
  Hydra 
  to 
  a 
  position 
  of 
  semi-extension, 
  

   after 
  a 
  contraction 
  reaction, 
  is 
  apparently 
  simply 
  a 
  return 
  to 
  

   the 
  position 
  of 
  rest. 
  Zoja 
  (1. 
  c.) 
  found 
  that 
  Hydra, 
  anassthe- 
  

  

  