﻿ON 
  SOJJE 
  MOVEMENTS 
  AND 
  EEACTIONS 
  OF 
  HIDEA. 
  613 
  

  

  off 
  from 
  them 
  as 
  completely 
  as 
  possible, 
  acd 
  filtered 
  Leef-tea 
  

   made 
  from 
  beef 
  extract 
  was 
  substituted. 
  Of 
  tlie 
  chemicals 
  in 
  

   meat 
  only 
  the 
  soluble 
  ones 
  can 
  stimulate 
  chemically, 
  and 
  

   these 
  are 
  well 
  represented 
  in 
  beef 
  extract. 
  So 
  if 
  the 
  stimulus 
  

   producing 
  a 
  food 
  reaction 
  weie 
  purely 
  chemical 
  Ave 
  might 
  

   expect 
  such 
  a 
  reaction 
  here. 
  

  

  But 
  there 
  Avas 
  no 
  trace 
  of 
  it 
  ; 
  the 
  Hydras 
  acted 
  exactly 
  as 
  

   they 
  did 
  in 
  ordinary 
  Avater, 
  except 
  Avhen 
  the 
  beef-tea 
  Avas 
  

   made 
  too 
  strong. 
  In 
  that 
  case 
  a 
  Hydra 
  contracted 
  just 
  as 
  it 
  

   does 
  in 
  the 
  case 
  of 
  any 
  other 
  chemical 
  in 
  strong 
  solution. 
  

   So 
  far 
  as 
  this 
  evidence 
  goes, 
  therefore, 
  a 
  chemical 
  stimulus 
  

   alone 
  is 
  no 
  more 
  adequate 
  to 
  produce 
  a 
  food 
  reaction 
  than 
  is 
  

   a 
  mechanical 
  one. 
  That 
  this 
  is 
  not 
  absolutely 
  true 
  Ave 
  shall 
  

   see 
  in 
  a 
  moment. 
  

  

  Next, 
  Ave 
  may 
  consider 
  the 
  efi'ect 
  of 
  a 
  combined 
  stimulus. 
  

   Some 
  of 
  the 
  Hydras 
  used 
  in 
  the 
  experiment 
  last 
  mentioned 
  

   Avere 
  returned 
  from 
  the 
  beef-tea 
  to 
  hydrant 
  water. 
  There 
  

   Avere 
  now 
  presented 
  to 
  them 
  minute 
  pieces 
  of 
  filter-paper 
  

   previously 
  soaked 
  in 
  beef-tea. 
  The 
  result 
  was 
  very 
  striking. 
  

   As 
  soon 
  as 
  the 
  paper 
  touched 
  the 
  tentacles 
  these 
  seized 
  it 
  and 
  

   drew 
  it 
  toAvard 
  the 
  liypostome. 
  As 
  soon 
  as 
  the 
  paper 
  touched 
  

   this 
  the 
  mouth 
  opened, 
  and 
  the 
  morsel 
  was 
  engulfed. 
  Here, 
  

   as 
  always, 
  no 
  effort 
  Avas 
  made 
  to 
  turn 
  the 
  object 
  in 
  any 
  Avay, 
  

   so 
  as 
  to 
  make 
  SAvallowing 
  it 
  easier. 
  The 
  Avay 
  it 
  was 
  pre- 
  

   sented 
  Avas 
  the 
  way 
  it 
  went 
  doAvn. 
  Such 
  a 
  piece 
  of 
  filter- 
  

   paper 
  is, 
  hoAvever, 
  usually 
  anything 
  but 
  smooth. 
  It 
  has 
  

   projecting 
  fibres 
  in 
  many 
  places, 
  and 
  these 
  projections, 
  after 
  

   the 
  paper 
  was 
  sAvallowed, 
  caused 
  the 
  body 
  Avail 
  of 
  Hydra 
  to 
  

   bulge 
  out 
  in 
  very 
  grotescjue 
  fashion. 
  The 
  same 
  experiment 
  

   was 
  repeated 
  many 
  times, 
  always 
  Avitli 
  the 
  same 
  result. 
  

  

  The 
  food 
  reaction 
  can 
  also 
  be 
  brought 
  about 
  by 
  immersino- 
  a 
  

   starved 
  Hydra 
  in 
  beef-tea, 
  and 
  then 
  stimulating 
  the 
  liypostome 
  

   mechanically 
  Avith 
  a 
  glass 
  rod. 
  The 
  reaction 
  does 
  not, 
  however, 
  

   appear 
  quite 
  as 
  constantly 
  as 
  in 
  the 
  previous 
  experiments. 
  

  

  Thus 
  Ave 
  see 
  that 
  by 
  properly 
  combining 
  a 
  chemical 
  stimulus 
  

   with 
  a 
  mechanical 
  one, 
  the 
  food 
  reaction 
  can 
  be 
  brought 
  

   about 
  in 
  Hydra 
  by 
  an 
  object 
  Avhich 
  itself 
  has 
  no 
  food 
  value. 
  

  

  