390 
Animal  Chemistry. 
furnace — the  food  is  the  fuel — the  excrements  are  the  ashes — and 
the  gases  exhaled  from  the  mouth  are  of  the  same  composition  as 
those  which  fly  up  the  chimney  of  the  furnace.”  If,  then,  we 
want  an  animal  to  lay  on  meat,  we  give  him  beans,  which  abound 
in  fibrine,  and  chopped  straw  for  fuel,  just  as  we  ourselves  eat  beef- 
steak and  potatoes.  Animals  seem  to  know  this  by  instinct,  for  my 
shepherd  tells  me  it  is  useless  to  give  the  sheep  chaff  in  their 
troughs  until  cold  weather  comes  on.  As  the  winter  deepens 
they  eat  more  chaff,  but  in  spring  gradually  leave  it  off,  till  in 
May  they  refuse  it,  as  we  light  our  fires  at  Michaelmas  and  leave 
our  grates  empty  in  May.  So  far  all  is  clear,  but  an  unfortunate 
doubt  remains  on  a point,  all-important  too  in  feeding  cattle, 
namely,  the  source  of  fat.  According  to  Liebig  it  is  the  surplus 
of  the  starchy  matter  in  food,  which,  not  being  wanted  for  fuel,  is 
not  consumed,  but  deposited  in  the  body  ready  for  future  use.  Dr. 
Playfair  compares  it  to  the  consumption  of  coal  in  e gas  retort, 
where,  if  there  be  not  air  enough  present,  a part  of  the  coal  in- 
stead of  passing  off  as  gas  is  left  behind  as  coal-tar.  The  tar 
formed  in  this  case,  says  that  agreeable  writer,  represents  the  fat 
of  animals.  If  this  be  so,  we  have  only  to  supply  our  fatting  hogs 
with  food  full  of  starch,  like  potatoes.  But  the  greatest  agricul- 
tural chemist,  Boussingault,  takes  a different  view  altogether.  He 
denies  that  fat  is  ever  produced  in  the  animal  frame  from  starch. 
He  shows  that  the  food  of  cattle  contains  a third  substance,  vege- 
table fat,  and  is  positive  that  as  the  flesh  of  animals  exists  ready 
formed  in  their  provender,  so  does  also  their  fat,  and  so  also  does 
the  butter  contained  in  their  milk.  On  the  latter  point  he  brings 
this  proof,  that  a cow,  namely,  being  fed  on  mangold-wurzel 
alone,  which  contains  little  fat,  gave  but  little  milk,  and  that  milk 
poor,  but  recovered  her  milk  on  receiving  straw  in  addition,  which, 
little  as  we  should  suppose  it,  contains  vegetable  fat.  Since  fat  is 
the  object  principally  aimed  at  in  preparing  stock  for  the  market, 
the  muscles  or  flesh  having  often,  1 suppose,  attained  their  full 
size  when  the  beast  is  put  up  to  feed,  it  is  evident  that,  until  the 
source  of  fat  be  determined,  organic  chemistry  being  undeter- 
mined itself,  can  give  no  certain  judgment  on  the  final  feeding  of 
stock.  I mean  that  we  can  have  no  reliable  tables  of  the  com- 
parative virtue  of  different  kinds  of  food  ; because,  if  Liebig  be 
right,  there  must  be  two  columns  of  figures,  1,  for  the  ingredients 
of  flesh, — 2,  for  those  of  fuel  and  fat  jointly  ; but  if  Boussingault, 
Dumas,  and  the  French  school  be  right,  then  we  must  consider 
each  article  of  food  under  the  three  heads  of  flesh,  fuel,  and 
fat  distinctly.  There  is  one  point,  however,  certain — the  import- 
ance of  warmth.  Wherever  fat  come  from,  there  is  no  doubt 
that  both  fat  and  flesh  are  wasted  from  the  production  of  beef  in 
an  animal  frame  suffering  by  excessive  cold.  The  substance  of  an 
