﻿ON 
  SOME 
  MOVEMENTS 
  AND 
  REACTIONS 
  OF 
  HYDRA. 
  607 
  

  

  strike 
  at 
  first 
  a 
  very 
  limited 
  area 
  on 
  the 
  surface 
  of 
  tlie 
  body. 
  

   In 
  other 
  words, 
  the 
  stimuli 
  was 
  distinctly 
  localised. 
  A 
  

   number 
  of 
  chemicals 
  were 
  experimented 
  with 
  in 
  this 
  manner 
  

   including" 
  citric 
  acid, 
  acetic 
  acid, 
  sodium 
  chloride, 
  sodium 
  

   carbonate, 
  potassium 
  bichromate, 
  methylene 
  bhie, 
  and 
  others. 
  

   The 
  action 
  of 
  all 
  was 
  precisely 
  the 
  same. 
  I 
  found, 
  however, 
  

   that 
  methyl 
  green 
  was 
  most 
  convenient 
  to 
  handle, 
  on 
  account 
  

   of 
  the 
  colour, 
  by 
  means 
  of 
  which 
  the 
  limits 
  of 
  the 
  diffusing 
  

   cloud, 
  were 
  easily 
  recognised, 
  and 
  because 
  it 
  gave 
  the 
  most 
  cer- 
  

   tain 
  results. 
  I 
  shall 
  describe 
  as 
  a 
  type, 
  therefore, 
  the 
  effects 
  

   obtained 
  by 
  the 
  use 
  of 
  this 
  substance. 
  That 
  the 
  results 
  

   obtained 
  were 
  due 
  to 
  chemical 
  action, 
  and 
  not 
  to 
  mechanical 
  

   agitation 
  is 
  shown 
  by 
  the 
  fact 
  that 
  no 
  effect 
  was 
  produced 
  by 
  

   streams 
  of 
  distilled 
  water 
  or 
  of 
  an 
  excessively 
  weak 
  solution 
  

   of 
  methyl 
  green 
  used 
  in 
  the 
  same 
  manner. 
  

  

  When 
  a 
  cloud 
  of 
  methyl 
  green 
  is 
  allowed 
  to 
  strike 
  Hydra 
  

   a 
  little 
  above 
  the 
  foot, 
  in 
  a 
  few 
  seconds 
  there 
  is 
  a 
  flexion 
  of 
  

   the 
  body 
  at 
  the 
  point 
  where 
  the 
  chemical 
  touches 
  it. 
  The 
  

   body 
  bends 
  over 
  slowly, 
  and 
  this 
  bending 
  is 
  toward 
  the 
  side 
  

   on 
  which 
  the 
  chemical 
  acts. 
  In 
  some 
  cases 
  there 
  is 
  also 
  a 
  

   sepai'ate 
  bending 
  just 
  below 
  the 
  hypostome, 
  toward 
  the 
  same 
  

   side. 
  This 
  latter 
  peculiar 
  movement 
  gives 
  the 
  appearance 
  of 
  

   the 
  presence 
  of 
  a 
  neck 
  region. 
  The 
  same 
  movement 
  has 
  

   been 
  observed 
  by 
  Pearl 
  ('01) 
  under 
  the 
  influence 
  of 
  the 
  

   electric 
  current, 
  and 
  it 
  can 
  also 
  be 
  observed 
  as 
  occurring 
  in 
  

   apparently 
  unstimulated 
  Hydra. 
  As 
  the 
  methyl 
  green 
  spreads 
  

   and 
  affects 
  a 
  larger 
  area 
  on 
  the 
  surface 
  of 
  the 
  Hydra 
  complete 
  

   contraction 
  results. 
  

  

  If 
  the 
  methyl 
  green 
  is 
  similarly 
  brought 
  near 
  to 
  the 
  middle 
  

   of 
  an 
  expanded 
  tentacle 
  the 
  tentacle 
  flexes 
  at 
  this 
  point 
  in 
  

   the 
  direction 
  from 
  which 
  the 
  chemical 
  approaches 
  it. 
  Then, 
  

   as 
  it 
  enters 
  the 
  denser 
  cloud 
  of 
  stain, 
  it 
  contracts. 
  The 
  

   tentacles 
  ai'e 
  decidedly 
  more 
  sensitive 
  to 
  the 
  action 
  of 
  the 
  

   chemicals 
  than 
  the 
  rest 
  of 
  the 
  body. 
  Usually 
  the 
  tentacle 
  

   flexes 
  before 
  the 
  visible 
  green 
  cloud 
  has 
  reached 
  it, 
  indicating 
  

   that 
  the 
  edges 
  of 
  this 
  cloud, 
  containing 
  yet 
  too 
  little 
  stain 
  to 
  

   be 
  visibly 
  coloured, 
  are 
  still 
  concentrated 
  enough 
  to 
  produce 
  

  

  