The  carbonic-acid  gas  puffs  up  the  dough  into  lightness,

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SOME  CHEMICAL  PROBLEMS  OF  TODAY

the  alcohol  has  a  similar  effect  in  the  oven,  and  in  ad-
dition checks  to  a  slight  extent  bacterial  fermentation,
and,  as  well,  has  a  softening  effect  upon  the  gluten  of  the
dough,  thus  increasing  its  power  to  hold  the  gas  which
is  produced.  The  bodies  of  these  little  organisms  con-
tain invertase,  which  is  able  to  convert  sugar-cane  into
invert  sugar;  they  contain  zymase,  which  is  the  sub-
stance that  transforms  the  sugars  so  produced  into  the
large  quantities  of  carbon-dioxide  and  alcohol;  and  they
contain,  as  well,  certain  other  ferments  that  convert  the
protein  matter  of  the  bread  into  material  of  grateful
taste  and  nutriment.  The  yeast  organisms  do  not  carry
out  this  work  per  se,  but  because  of  these  substances
they  contain.  In  order  that  they  may  rapidly  multiply
to  efficient  working,  the  dough  contains,  almost  provi-
dentially one  might  say,  the  requisite  substances —
soluble  proteids  to  afford  them  nitrogenous  food,  sugar,
without  which  they  will  not  work  at  all,  and  mineral
substances  which  accelerate  their  action.  All  this  is
very  pretty  philosophy,  what  we  know  of  it,  but,  as  a
matter  of  fact,  the  very  outposts  of  a  true  knowledge  of
bread-making  still  remain  unconquered.
