which  constitutes  so  vast  and  plain  a  distinction  between  living
bodies  and  those  which  do  not  live  is  an  ultimate  fact :  indicating,
as  such,  the  existence  of  a  broad  line  of  demarcation  between  the
subject-matter  of  biological  and  that  of  all  other  sciences."

Between  1854  and  the  publication  of  the  essay  "On  the  Physical
Basis  of  Life"  in  1868,  natural  science  advanced  with  strides  which
have  no  parallel,  and  the  "  Origin  of  Species "  brought  about  a
revolution  in  our  conceptions  of  the  history  of  living  nature. It
is  not  surprising  that  Huxley's  point  of  view  undergoes  significant
change,  and  that  a  new  aspect  of  nature  now  excites  his  interest
and  absorbs  his  attention. The  establishment  of  the  doctrine  of
the  continuity  of  life  on  a  firm  basis,  and  the  acceptance  of  the
generalization  that  all  living  things  are  related  by  birth,  had  given
new  meaning  to  the  familiar  truth  that  they  are  all  fundamentally
identical  in  structure  ;  and  the  essay  of  1868  deals  with  this  aspect
of  living  organisms. The  essay  is  regarded  by  many  readers  —
both  those  who  look  upon  it  with  horror  and  those  who  make  it
the  basis  of  a  biological  creed — as  contradictory  to  the  essay  of
1854;  but  I,  for  one,  am  unable  to  find  in  it  any  basis  for  this
opinion. Its  motive  —  the  truth  that  "protoplasm  is  the  basis  of
life";  that  "it  is  the  clay  of  the  potter,  which,  bake  it  and  paint


HUXLEV,   AND   THE  PROBLEM  OF  THE  NATURALIST       37

it  as  he  will,  remains  clay,  separated  by  artifice  and  not  by  nature
from  the  commonest  brick  or  sundried  clod,"  is  no  novelty. 