﻿The 
  Properties 
  of 
  Colloidal 
  Systems. 
  

  

  199 
  

  

  value. 
  If 
  too 
  strong, 
  the 
  organism 
  u 
  explodes," 
  driving 
  out 
  its 
  contents 
  into 
  

   the 
  water, 
  where 
  they 
  rapidly 
  become 
  dispersed. 
  But 
  even 
  if 
  the 
  current 
  is 
  

   not 
  strong 
  enough 
  to 
  produce 
  any 
  immediate 
  effect, 
  it 
  is 
  necessary 
  to 
  cut 
  it 
  

   off 
  the 
  moment 
  that 
  any 
  trace 
  of 
  contraction 
  or 
  other 
  effect 
  shows 
  itself. 
  

   A 
  very 
  weak 
  current, 
  if 
  left 
  on 
  for 
  a 
  sufficiently 
  long 
  time, 
  kills 
  with 
  

   disintegration. 
  Moreover, 
  the 
  protoplasm 
  may 
  be 
  " 
  killed," 
  in 
  the 
  sense 
  of 
  

   permanent 
  cessation 
  of 
  movement, 
  although 
  no 
  immediate 
  breaking 
  up 
  may 
  

   take 
  place. 
  Since, 
  therefore, 
  if 
  recovery 
  is 
  to 
  be 
  expected, 
  it 
  is 
  not 
  per- 
  

   missible 
  to 
  continue 
  the 
  stimulus 
  for 
  more 
  than 
  a 
  brief 
  time, 
  the 
  observations 
  

   must 
  be 
  made 
  rapidly. 
  

  

  It 
  is 
  a 
  comparatively 
  simple 
  matter 
  to 
  convince 
  oneself 
  of 
  the 
  correctness 
  

   of 
  Kuhne's 
  statement 
  with 
  regard 
  to 
  the 
  cessation 
  of 
  the 
  flowing 
  movements 
  

   of 
  the 
  larger 
  granules 
  into 
  and 
  out 
  of 
  the 
  pseudopodia. 
  This 
  is, 
  no 
  doubt,, 
  

   rightly 
  stated 
  to 
  be 
  due 
  to 
  the 
  " 
  contraction 
  " 
  of 
  the 
  organism 
  into 
  a 
  more 
  

   or 
  less 
  spherical 
  shape, 
  with 
  simultaneous 
  arrest 
  of 
  the 
  protrusion 
  and 
  

   retraction 
  of 
  the 
  pseudopodia. 
  But 
  it 
  is 
  clear 
  that 
  this 
  observation 
  does 
  not 
  

   necessarily 
  imply 
  a 
  change 
  of 
  the 
  protoplasm 
  into 
  the 
  gel 
  state. 
  This 
  latter 
  

   can 
  only 
  be 
  tested 
  by 
  examination 
  of 
  the 
  Brownian 
  movements 
  of 
  the 
  minute 
  

   particles 
  visible 
  by 
  dark 
  -ground 
  illumination. 
  The 
  most 
  satisfactory 
  place 
  

   to 
  make 
  this 
  observation 
  is 
  the 
  clear 
  protoplasm 
  of 
  the 
  outer 
  part 
  of 
  the 
  

   pseudopodia, 
  which 
  is 
  free 
  from 
  the 
  to-and-fro 
  movement 
  of 
  the 
  large 
  

   granules 
  of 
  the 
  central 
  protoplasmic 
  mass. 
  It 
  is 
  generally 
  possible 
  to 
  make 
  

   use 
  of 
  a 
  stimulus 
  not 
  strong 
  enough 
  to 
  cause 
  sudden 
  retraction 
  of 
  the 
  

   pseudopodium 
  as 
  a 
  whole. 
  In 
  a 
  successful 
  experiment, 
  the 
  effect 
  is 
  very 
  

   striking. 
  The 
  continuous 
  shimmering 
  tremulous 
  movement 
  of 
  the 
  bright 
  

   points, 
  due 
  to 
  their 
  Brownian 
  movement, 
  ceases 
  almost 
  instantaneously, 
  as 
  

   if 
  the 
  liquid 
  protoplasm 
  had 
  been 
  frozen. 
  As 
  soon 
  as 
  this 
  happens, 
  the 
  

   stimulation 
  is 
  stopped, 
  and, 
  apparently, 
  almost 
  at 
  the 
  same 
  time, 
  the 
  

   Brownian 
  movement 
  and 
  the 
  flowing 
  pseudopodial 
  extrusion 
  recommence. 
  

  

  It 
  is 
  significant 
  that 
  the 
  Brownian 
  movement 
  does 
  not 
  cease 
  during 
  

   natural 
  pseudopodial 
  movement 
  of 
  the 
  protoplasm. 
  This 
  fact 
  might, 
  perhaps, 
  

   be 
  regarded, 
  especially 
  by 
  those 
  who 
  look 
  upon 
  the 
  gel 
  state 
  as 
  an 
  accom- 
  

   paniment 
  of 
  cell 
  activity 
  in 
  general, 
  as 
  evidence 
  that 
  the 
  protrusion 
  of 
  

   pseudopodia 
  is 
  the 
  result 
  of 
  differences 
  of 
  surface 
  tension 
  at 
  the 
  contact 
  

   between 
  protoplasm, 
  water, 
  and 
  solid 
  surface 
  on 
  which 
  the 
  organism 
  rests. 
  

   But 
  the 
  mode 
  of 
  production 
  of 
  pseudopodia 
  is 
  as 
  yet 
  a 
  matter 
  of 
  dispute. 
  

  

  If 
  the 
  electrical 
  shock 
  in 
  the 
  experiments 
  described 
  above 
  has 
  been 
  too 
  

   strong, 
  so 
  that 
  the 
  organism 
  is 
  killed, 
  but 
  not 
  so 
  strong 
  that 
  " 
  explosion 
  " 
  

   takes 
  place, 
  the 
  fixed 
  state 
  of 
  gelation 
  is 
  permanent 
  ; 
  the 
  sol 
  state 
  does 
  

   not 
  return 
  until 
  disintegration 
  sets 
  in. 
  This 
  is 
  in 
  agreement 
  with 
  the 
  

  

  