﻿92 
  THE 
  CRITERIA 
  OF 
  LIVINGNESS 
  

  

  of 
  reproduction 
  ! 
  Perhaps 
  we 
  are 
  looking 
  back 
  to 
  near 
  the 
  

   beginning 
  of 
  organic 
  life 
  when 
  we 
  see 
  the 
  fragmentation 
  

   of 
  a 
  protoplasmic 
  corpuscle 
  which 
  has 
  grown 
  too 
  large 
  to 
  

   be 
  a 
  successful 
  unity. 
  It 
  cannot 
  be 
  gainsaid 
  that 
  the 
  division 
  

   of 
  a 
  cell 
  remains 
  one 
  of 
  the 
  mysteries 
  of 
  the 
  world. 
  Professor 
  

   Bateson 
  writes 
  (1913, 
  p. 
  39): 
  "I 
  know 
  nothing 
  which 
  to 
  

   a 
  man 
  well 
  trained 
  in 
  scientific 
  knowledge 
  and 
  method 
  brings 
  

   so 
  vivid 
  a 
  realisation 
  of 
  our 
  ignorance 
  of 
  the 
  nature 
  of 
  

   life 
  as 
  the 
  mystery 
  of 
  cell-division. 
  . 
  . 
  . 
  It 
  is 
  this 
  power 
  

   of 
  spontaneous 
  division 
  which 
  most 
  sharply 
  distinguishes 
  

   the 
  living 
  from 
  the 
  non-living. 
  . 
  . 
  . 
  The 
  greatest 
  advance 
  

   I 
  can 
  conceive 
  in 
  biology 
  would 
  be 
  the 
  discovery 
  of 
  the 
  

   instability 
  which 
  leads 
  to 
  the 
  continual 
  division 
  of 
  the 
  cell. 
  

   When 
  I 
  look 
  at 
  a 
  dividing 
  cell 
  I 
  feel 
  as 
  an 
  astronomer 
  might 
  

   do 
  if 
  he 
  beheld 
  the 
  formation 
  of 
  a 
  double 
  star: 
  that 
  an 
  

   original 
  act 
  of 
  creation 
  is 
  taking 
  place 
  before 
  me." 
  

  

  In 
  most 
  cases 
  the 
  cell 
  divides 
  into 
  two 
  precisely 
  similar 
  

   daughter-cells, 
  this 
  being 
  associated 
  with 
  an 
  exceedingly 
  

   complicated 
  division 
  of 
  the 
  nucleus, 
  which 
  secures 
  that 
  each 
  

   of 
  the 
  two 
  daughter-cells 
  gets 
  a 
  meticulously 
  precise 
  half 
  

   of 
  the 
  chromatin 
  material 
  of 
  the 
  original 
  nucleus. 
  But 
  

   the 
  difficulty 
  of 
  the 
  problem 
  is 
  increased 
  by 
  the 
  fact 
  that 
  

   a 
  cell 
  may 
  also 
  divide 
  into 
  two 
  dissimilar 
  halves, 
  as 
  appears 
  

   to 
  happen 
  in 
  certain 
  modes 
  of 
  inheritance. 
  In 
  exceptional 
  

   cases 
  among 
  multicellular 
  organisms 
  the 
  process 
  of 
  cell- 
  

   division 
  is 
  simpler 
  and 
  more 
  direct, 
  and 
  in 
  some 
  unicellular 
  

   organisms 
  it 
  is 
  very 
  simple. 
  It 
  is 
  probable 
  that 
  the 
  com- 
  

   plicated 
  methods 
  of 
  cell-division 
  which 
  are 
  now 
  the 
  rule 
  

   are 
  the 
  results 
  of 
  a 
  long 
  process 
  of 
  evolution, 
  and 
  that 
  the 
  

   fundamental 
  characteristic 
  is 
  simply 
  division. 
  But 
  why 
  

   should 
  the 
  protoplasmic 
  unit 
  divide 
  ? 
  Spencer, 
  Leuckart, 
  

   and 
  James 
  pointed 
  out 
  independently 
  that, 
  as 
  a 
  cell 
  of 
  

  

  