﻿612 
  GEORGE 
  WAGNER. 
  

  

  hunger, 
  althongli 
  the 
  food 
  takiug 
  was. 
  lu 
  the 
  protozoans 
  

   even 
  food 
  taking 
  (swallowing) 
  is 
  seemingly 
  a 
  continuous 
  

   process. 
  One 
  sometimes 
  sees 
  Paramecia 
  with 
  bodies 
  crowded 
  

   with 
  food 
  material 
  still 
  steadily 
  taking 
  in 
  more. 
  

  

  The 
  Hydras 
  used 
  in 
  subsequent 
  work 
  were 
  therefore 
  starved 
  

   for 
  a 
  period 
  of 
  seven 
  or 
  eight 
  days 
  by 
  keeping 
  them 
  in 
  fil- 
  

   tered 
  water. 
  There 
  is 
  a 
  remarkable 
  increase 
  in 
  activity 
  in 
  

   such 
  Hydras. 
  Their 
  tentacles 
  are 
  in 
  almost 
  constant 
  and 
  

   rather 
  rapid 
  motion, 
  and 
  the 
  body 
  sways 
  to 
  and 
  fro, 
  expands 
  

   and 
  contracts, 
  in 
  a 
  very 
  nervous 
  manner. 
  Green 
  Hydras 
  

   stand 
  starving 
  very 
  poorly, 
  usually 
  perishing 
  in 
  two 
  or 
  three 
  

   daj^s. 
  I 
  therefore 
  used 
  Hydra 
  grisea 
  for 
  this 
  part 
  of 
  the 
  

   work. 
  Its 
  larger 
  size 
  gives 
  it 
  another 
  advantage. 
  

  

  Let 
  us 
  now 
  consider 
  what 
  factors 
  in 
  the 
  food 
  enable 
  the 
  

   Hydras 
  to 
  recognise 
  it 
  as 
  such. 
  It 
  is 
  evident 
  that 
  any 
  stimu- 
  

   lus 
  coming 
  from, 
  say, 
  a 
  piece 
  of 
  meat 
  must 
  be 
  either 
  chemical 
  

   or 
  mechanical. 
  

  

  Let 
  us 
  consider 
  the 
  mechanical 
  stimulus 
  first. 
  The 
  result 
  

   of 
  experiments 
  directed 
  to 
  this 
  point 
  could 
  be 
  foreseen. 
  In 
  

   studying 
  the 
  effect 
  of 
  mechanical 
  stimuli 
  several 
  hundred 
  

   Hydras, 
  from 
  many 
  sources, 
  were 
  stimulated 
  by 
  prodding 
  

   with 
  glass 
  rods 
  on 
  every 
  part 
  of 
  the 
  body, 
  including 
  hypos- 
  

   tome 
  and 
  tentacles, 
  and 
  at 
  all 
  degrees 
  of 
  intensity. 
  In 
  no 
  

   case 
  did 
  there 
  result 
  any 
  reaction 
  resembling 
  in 
  any 
  way 
  

   the 
  movements 
  concerned 
  in 
  feeding. 
  To 
  make 
  sui^e, 
  how- 
  

   ever, 
  I 
  tested 
  Hydra 
  that 
  had 
  been 
  starved 
  for 
  from 
  seven 
  to 
  

   tea 
  days 
  by 
  placing 
  minute 
  bits 
  of 
  filter-paper 
  on 
  the 
  hypos- 
  

   tome. 
  This 
  paper 
  had 
  been 
  soaked 
  for 
  several 
  days 
  in 
  water 
  

   from 
  exactly 
  the 
  same 
  source 
  as 
  that 
  in 
  which 
  the 
  Hydra 
  

   were 
  kept 
  while 
  starving. 
  All 
  possibility 
  of 
  chemical 
  stimu- 
  

   lation 
  was 
  thus 
  removed. 
  The 
  result 
  was 
  as 
  expected. 
  There 
  

   was 
  no 
  trace 
  of 
  a 
  food 
  reaction, 
  and 
  the 
  paper 
  soon 
  rolled 
  

   away 
  from 
  the 
  animal. 
  A 
  mechanical 
  stimulus 
  alone, 
  then, 
  

   cannot 
  call 
  forth 
  a 
  food 
  reaction. 
  

  

  Is 
  the 
  same 
  thing 
  true 
  of 
  a 
  chemical 
  stimulus 
  ? 
  To 
  test 
  

   this 
  I 
  took 
  Hydras, 
  starved 
  for 
  seven 
  or 
  eight 
  days, 
  and 
  

   placed 
  them 
  in 
  small 
  watch-glasses. 
  The 
  water 
  was 
  drawn 
  

  

  