﻿OF 
  THE 
  DOCTRINE 
  OF 
  VITAL 
  AFFINITY. 
  393 
  

  

  still 
  farther 
  diminished 
  from 
  their 
  alternate 
  contraction 
  from 
  the 
  stimulus 
  of 
  the 
  

   blood. 
  There 
  can 
  be 
  no 
  doubt 
  that 
  in 
  compounds 
  the 
  force 
  of 
  attraction 
  subsist- 
  

   ing 
  among 
  their 
  constituent 
  particles, 
  is 
  modified 
  by 
  the 
  distance 
  at 
  which 
  these 
  

   are 
  placed 
  ; 
  and 
  in 
  compounds 
  especially, 
  which 
  consist 
  of 
  four 
  or 
  more 
  prin- 
  

   ciples, 
  the 
  slightest 
  alteration 
  in 
  their 
  relative 
  situation 
  is 
  sufficient 
  to 
  change 
  

   entirely 
  their 
  existing 
  attraction, 
  and 
  induce 
  new 
  combinations. 
  The 
  blood 
  is 
  a 
  

   compound 
  of 
  this 
  kind 
  ; 
  its 
  ultimate 
  principles, 
  too, 
  are 
  capable 
  of 
  entering 
  into 
  

   an 
  innumerable 
  variety 
  of 
  combinations 
  with 
  each 
  other 
  ; 
  we 
  may 
  conceive, 
  

   therefore, 
  that 
  when 
  subjected 
  to 
  the 
  contraction 
  of 
  the 
  extremely 
  minute 
  vessels 
  

   through 
  which 
  it 
  is 
  forced 
  to 
  circulate, 
  the 
  relative 
  position 
  of 
  its 
  elements 
  will 
  be 
  

   changed, 
  and 
  new 
  combinations 
  formed. 
  And 
  if 
  we 
  suppose 
  a 
  fluid 
  thus 
  passing 
  

   through 
  tubes 
  of 
  different 
  diameters, 
  and 
  undergoing 
  successive 
  decompositions, 
  

   we 
  may 
  easily 
  conceive 
  that 
  very 
  different 
  products 
  may 
  be 
  formed 
  from 
  the 
  

   same 
  original 
  compound. 
  This 
  affords 
  a 
  very 
  simple 
  view 
  of 
  the 
  nature 
  of 
  Secre- 
  

   tion. 
  No 
  complicated 
  apparatus 
  is 
  requisite 
  ; 
  all 
  that 
  is 
  necessary 
  being 
  the 
  pro- 
  

   pulsion 
  of 
  the 
  blood 
  through 
  extremely 
  minute 
  vessels 
  capable 
  of 
  contraction. 
  

   And 
  it 
  is 
  easy 
  to 
  account 
  for 
  the 
  variations 
  to 
  which 
  secretion 
  is 
  liable, 
  as 
  the 
  

   contraction 
  of 
  the 
  vessels 
  must 
  vary 
  from 
  variations 
  in 
  the 
  state 
  of 
  their 
  irritabi- 
  

   lity 
  and 
  of 
  the 
  stimuli 
  acting 
  on 
  them." 
  [Murray's 
  System 
  of 
  Chemistry, 
  vol. 
  iv., 
  

   p. 
  518.] 
  In 
  regard 
  to 
  the 
  Nutrition 
  of 
  solids, 
  Dr 
  Murray 
  says 
  merely 
  that 
  they 
  

   appear 
  to 
  attract 
  immediately 
  from 
  the 
  blood 
  the 
  materials 
  which 
  it 
  contains 
  ready 
  

   formed, 
  as 
  there 
  is 
  probably 
  '•' 
  no 
  solid 
  in 
  the 
  animal 
  body, 
  of 
  which 
  the 
  imme- 
  

   diate 
  principles 
  do 
  not 
  exist 
  in 
  the 
  blood." 
  [Ibid., 
  p. 
  516.] 
  But 
  I 
  need 
  hardly 
  

   say 
  that 
  subsequent 
  researches 
  have 
  not 
  only 
  completely 
  demonstrated 
  the 
  insuf- 
  

   ficiency 
  of 
  this 
  explanation, 
  but 
  have 
  shewn 
  that 
  the 
  cause 
  of 
  the 
  difference 
  of 
  

   products 
  formed 
  apparently 
  from 
  the 
  same 
  blood 
  must 
  be 
  essentially 
  different 
  

   from 
  that 
  here 
  assigned 
  ; 
  and 
  I 
  would 
  say 
  farther, 
  have 
  shewn 
  that 
  the 
  pecu- 
  

   liarity 
  of 
  the 
  compounds 
  formed 
  in 
  living 
  bodies 
  cannot 
  be 
  reasonably 
  ascribed 
  to 
  

   any 
  modification 
  of 
  those 
  movements 
  of 
  fluids, 
  which 
  Dr 
  Daubeny 
  regards 
  as 
  the 
  

   only 
  results 
  of 
  the 
  vital 
  principle. 
  To 
  shew 
  this, 
  I 
  need 
  not 
  go 
  into 
  the 
  question 
  

   of 
  the 
  mode 
  of 
  action 
  of 
  arteries 
  on 
  the 
  blood, 
  or 
  the 
  portion 
  of 
  the 
  changes 
  essen- 
  

   tial 
  to 
  secretion, 
  which 
  takes 
  place 
  in 
  cells, 
  exterior 
  to 
  vessels, 
  and, 
  of 
  course, 
  can- 
  

   not 
  be 
  ascribed 
  merely 
  to 
  the 
  pressure 
  to 
  which 
  the 
  blood 
  passing 
  along 
  the 
  vessels 
  

   may 
  have 
  been 
  subjected 
  ; 
  which 
  had 
  certainly 
  been 
  misapprehended 
  by 
  Murray, 
  

   as 
  by 
  most 
  other 
  physiologists 
  of 
  that 
  day. 
  It 
  is 
  sufficient 
  to 
  quote 
  a 
  brief 
  state- 
  

   ment 
  from 
  Cuvier, 
  which 
  seems 
  to 
  me 
  quite 
  conclusive 
  as 
  to 
  the 
  question, 
  

   whether 
  difference 
  of 
  secreted 
  fluids 
  in 
  the 
  animal 
  economy 
  can 
  be 
  ascribed 
  to 
  

   difference 
  in 
  the 
  structure 
  of, 
  and 
  therefore 
  of 
  the 
  movement 
  of 
  the 
  blood 
  through, 
  

   the 
  organs 
  in 
  which 
  they 
  appear. 
  " 
  The 
  same 
  organ," 
  he 
  says, 
  i.e., 
  the 
  organ 
  

   secreting 
  the 
  same 
  fluid 
  from 
  the 
  blood, 
  "presents 
  in 
  different 
  classes 
  of 
  animals, 
  

   sometimes 
  in 
  the 
  same 
  class, 
  perfectly 
  distinct 
  structures. 
  This 
  is 
  true 
  of 
  the 
  

   V^OL. 
  xx. 
  part 
  in. 
  5 
  o 
  

  

  