﻿THE 
  CRITERIA 
  OF 
  LIVINGNESS 
  93 
  

  

  regular 
  shape 
  increases 
  in 
  volume, 
  it 
  does 
  not 
  proportionately 
  

   increase 
  in 
  surface. 
  If 
  it 
  be 
  a 
  sphere, 
  the 
  volume 
  of 
  material 
  

   to 
  be 
  kept 
  alive 
  increases 
  as 
  the 
  cube 
  of 
  the 
  radius, 
  while 
  

   the 
  surface, 
  through 
  which 
  the 
  keeping 
  alive 
  is 
  effected, 
  in- 
  

   creases 
  only 
  as 
  the 
  square. 
  Thus 
  there 
  tends 
  to 
  be 
  a 
  hazard- 
  

   ous 
  disproportion 
  between 
  volume 
  and 
  surface, 
  which 
  may 
  

   set 
  up 
  instability. 
  The 
  disturbed 
  balance 
  may 
  be 
  restored 
  

   by 
  the 
  emission 
  of 
  processes 
  from 
  the 
  surface 
  of 
  the 
  cell, 
  

   making 
  it 
  like 
  a 
  country 
  with 
  a 
  big 
  coast-line, 
  as 
  in 
  Rhizopod 
  

   Protozoa 
  or 
  in 
  the 
  amoeboid 
  cells 
  found 
  in 
  most 
  multicellular 
  

   animals. 
  But 
  the 
  disturbed 
  balance 
  is 
  normally 
  restored 
  

   by 
  the 
  cell 
  dividing 
  into 
  two 
  cells. 
  This 
  view 
  indicates 
  the 
  

   advantage 
  of 
  cell-division, 
  but 
  beyond 
  the 
  hint 
  that 
  a 
  dis- 
  

   proportion 
  between 
  volume 
  and 
  surface 
  may 
  induce 
  physio- 
  

   logical 
  instability, 
  perhaps 
  a 
  cell-solution 
  or 
  cytolysis, 
  it 
  

   does 
  not 
  tell 
  us 
  what 
  brings 
  the 
  process 
  about. 
  

  

  It 
  is 
  an 
  interesting 
  fact 
  that 
  if 
  a 
  non-nucleated 
  fragment 
  

   of 
  cell-substance 
  be 
  cut 
  off 
  from 
  a 
  large 
  Protozoon, 
  it 
  can 
  

   move 
  about 
  for 
  a 
  time, 
  but 
  it 
  cannot 
  feed 
  or 
  grow, 
  and 
  

   sooner 
  or 
  later 
  it 
  dies. 
  But 
  a 
  nucleated 
  fragment 
  does 
  not 
  

   'die. 
  There 
  are 
  other 
  facts 
  which 
  point 
  to 
  the 
  same 
  conclu- 
  

   sion 
  that 
  the 
  nucleus 
  is 
  a 
  sort 
  of 
  dynamic 
  centre 
  to 
  the 
  cell 
  

   (especially 
  a 
  trophic 
  centre), 
  and 
  that 
  stability 
  depends 
  on 
  

   keeping 
  up 
  a 
  certain 
  proportion 
  or 
  relation 
  between 
  the 
  

   nucleoplasm 
  and 
  the 
  cytoplasm. 
  It 
  follows, 
  therefore, 
  that 
  

   if 
  growth 
  imply 
  an 
  increase 
  of 
  cell-substance 
  out 
  of 
  pro- 
  

   portion 
  to 
  nuclear 
  substance, 
  a 
  state 
  of 
  physiological 
  in- 
  

   stability 
  may 
  set 
  in, 
  which 
  cell-division 
  may 
  counteract. 
  

   In 
  many 
  large 
  Protozoa 
  there 
  are 
  numerous 
  nuclei. 
  

  

  It 
  has 
  also 
  been 
  suggested 
  that 
  a 
  period 
  of 
  growth 
  is 
  auto- 
  

   matically 
  followed 
  by 
  a 
  process 
  of 
  " 
  autokatalysis 
  ", 
  or 
  self- 
  

   fermentation, 
  but 
  precise 
  data 
  are 
  awanting. 
  What 
  we 
  wish 
  

  

  