﻿OF 
  THE 
  DOCTRINE 
  OF 
  VITAL 
  AFFINITY. 
  395 
  

  

  Liebig 
  himself, 
  that 
  the 
  infusory 
  animals 
  decompose 
  the 
  carbonic 
  acid 
  of 
  the 
  air, 
  

   and 
  exhale 
  oxygen 
  in 
  like 
  manner 
  as 
  vegetables 
  ; 
  and 
  the 
  evidence 
  of 
  the 
  forma- 
  

   tion 
  of 
  oily 
  out 
  of 
  saccharine 
  or 
  amylaceous 
  matters 
  in 
  many 
  animals 
  appears 
  to 
  

   be 
  unequivocal. 
  The 
  two 
  distinct 
  powers, 
  therefore, 
  of 
  forming 
  and 
  of 
  fixing, 
  or 
  

   appropriating 
  the 
  organic 
  compounds, 
  are 
  not 
  so 
  accurately 
  divided 
  between 
  the 
  

   vegetable 
  and 
  animal 
  world 
  as 
  has 
  been 
  thought. 
  But 
  the 
  more 
  that 
  any 
  physio- 
  

   logist 
  is 
  convinced, 
  as 
  Dr 
  Daubeny 
  is, 
  that 
  the 
  formation 
  of 
  organic 
  compounds 
  is 
  

   peculiar 
  to 
  vegetables, 
  certainly 
  the 
  less 
  reason 
  can 
  he 
  have 
  for 
  supposing 
  that 
  

   this 
  great 
  change 
  can 
  be 
  due 
  to 
  any 
  mechanical 
  movements, 
  on 
  the 
  principle 
  of 
  

   contraction 
  and 
  impulse, 
  arising 
  out 
  of 
  the 
  vital 
  principle 
  ; 
  the 
  provisions 
  for 
  such 
  

   movements 
  being 
  so 
  striking 
  a 
  part 
  of 
  the 
  economy 
  of 
  animals, 
  and 
  never 
  having 
  

   been 
  proved 
  to 
  exist 
  at 
  all 
  in 
  vegetables. 
  

  

  But, 
  secondly, 
  In 
  maintaining 
  the 
  scientific 
  correctness 
  of 
  the 
  doctrine 
  of 
  

   vital 
  affinity, 
  as 
  I 
  have 
  defined 
  it, 
  I 
  think 
  it 
  quite 
  unnecessary 
  to 
  go 
  into 
  these 
  

   details. 
  I 
  maintain 
  that 
  the 
  objections 
  made 
  to 
  this 
  doctrine, 
  both 
  by 
  Dau- 
  

   beny 
  and 
  Humboldt, 
  are 
  logically 
  incorrect, 
  because, 
  in 
  dealing 
  with 
  a 
  set 
  of 
  

   facts 
  so 
  extraordinary, 
  so 
  important 
  and 
  characteristic 
  as 
  the 
  chemical 
  changes 
  

   of 
  living 
  beings 
  have 
  been 
  shewn 
  • 
  to 
  be, 
  they 
  hold 
  it 
  to 
  be 
  incumbent 
  on 
  us 
  

   to 
  prove 
  the 
  negative 
  proposition, 
  that 
  these 
  may 
  not 
  ultimately 
  be 
  referred 
  to 
  

   those 
  laws 
  which 
  regulate 
  the 
  chemical 
  changes 
  in 
  dead 
  matter, 
  which 
  may 
  be 
  

   acting 
  under 
  conditions 
  not 
  yet 
  known, 
  and 
  of 
  which 
  they 
  say 
  nothing. 
  The 
  

   rule 
  of 
  sound 
  logic 
  is, 
  — 
  " 
  affirmantibus 
  incumbit 
  probatio." 
  It 
  is 
  admitted 
  on 
  

   all 
  hands, 
  that 
  the 
  phenomena 
  of 
  life 
  in 
  general 
  are 
  so 
  peculiar 
  and 
  important 
  

   as 
  to 
  be 
  properly 
  ranked 
  together 
  as 
  a 
  separate 
  science 
  ; 
  and 
  we 
  have 
  shewn 
  that 
  

   of 
  these 
  phenomena, 
  the 
  most 
  essential 
  and 
  characteristic 
  are 
  certain 
  chemical 
  

   changes, 
  which 
  are 
  admitted 
  to 
  be 
  so 
  distinct 
  from 
  any 
  that 
  can 
  be 
  observed 
  any- 
  

   where 
  else 
  in 
  nature 
  as 
  to 
  " 
  indicate 
  the 
  existence 
  of 
  a 
  power 
  distinct 
  from 
  any 
  

   simply 
  chemical 
  or 
  physical 
  forces." 
  It 
  is 
  clearly 
  incumbent 
  on 
  those 
  who 
  main- 
  

   tain 
  that, 
  nevertheless, 
  these 
  ordinary 
  chemical 
  forces, 
  acting 
  under 
  conditions 
  

   not 
  yet 
  understood, 
  may 
  be 
  found 
  adequate 
  to 
  this 
  explanation, 
  to 
  give 
  evidence 
  

   in 
  the 
  way 
  of 
  observation 
  and 
  experiment 
  of 
  this 
  proposition, 
  otherwise 
  their 
  

   doctrine 
  is 
  only 
  a 
  hypothesis. 
  If 
  the 
  subject 
  is 
  not 
  thought 
  worthy 
  of 
  scientific 
  

   inquiry 
  at 
  all, 
  then 
  Physiology 
  is 
  not 
  a 
  separate 
  science. 
  If 
  it 
  is 
  regarded 
  as 
  a 
  

   separate 
  science, 
  of 
  equal 
  interest 
  and 
  importance 
  as 
  any 
  other, 
  then 
  it 
  is 
  the 
  

   duty 
  of 
  physiologists, 
  acting 
  on 
  the 
  strict 
  method 
  of 
  induction, 
  — 
  because 
  ascend- 
  

   ing 
  from 
  facts 
  to 
  principles, 
  instead 
  of 
  descending 
  from 
  principles 
  to 
  facts, 
  — 
  to 
  

   examine 
  these 
  individual 
  phenomena 
  themselves, 
  arrange 
  and 
  classify 
  them 
  as 
  

   they 
  present 
  themselves 
  in 
  the 
  different 
  classes 
  of 
  living 
  beings, 
  and 
  consider 
  how 
  

   far 
  laws 
  deduced 
  from 
  the 
  observation 
  of 
  dead 
  matter 
  can 
  go 
  in 
  the 
  explanation 
  of 
  

   them 
  ; 
  but 
  wherever 
  we 
  find 
  that 
  there 
  is 
  a 
  difficulty 
  in 
  that 
  explanation, 
  — 
  in- 
  

  

  