ON  FERMENTATION. 
333 
of  10  grammes  of  sugar  within  nine  days,  and  the  yeast  devel- 
oped was  also  exhausted. 
It  appears,  therefore,  that,  by  bringing  about  the  conversion 
of  the  soluble  portion  of  yeast  into  organized  globules,  a  quan- 
tity of  sugar  may  be  decomposed  which  is  nearly  equal  to  that 
decomposed  by  the  action  of  an  equivalent  quantity  of  the  yeast 
in  its  natural  state.  The  difference  between  the  two  quantities 
of  sugar  fermented  in  the  above  instance  appears,  moreover, 
easily  explicable.  The  developement  of  globules  in  the  very 
dilute  decoction  of  yeast  may  be  expected  to  be  retarded,  and 
the  extraction  with  water  would  probably  not  effect  the  separa- 
tion of  all  the  soluble  portion  of  the  yeast  probably  confined 
within  the  globules. 
These  results  are  directly  connected  with  the  explication  of 
facts  relating  to  the  history  of  fermentation  that  have  always 
appeared  extraordinary.  M.  Thenard  long  since  observed  that 
yeast  may  be  dried  at  212°  F.,  or  heated  to  the  boiling  point, 
without  its  efficacy  as  a  ferment  being  sensibly  diminished.  The 
sole  peculiarity  of  its  action  under  these  circumstances,  consists 
in  the  commencement  and  progress  of  the  fermentation  being 
slower  than  when  the  same  yeast  is  used  in  the  fresh  state. 
These  curious  facts  have  been  put  forward  by  those  chemists  who 
adopt  the  views  of  Liebig  and  Berzelius,  and  deny  the  influence 
of  organization  as  a  cause  of  the  phenomena  of  fermentation. 
It  was  argued,  that  exposure  to  a  temperature  of  212°  F., 
whether  combined  with  prolonged  drying  or  not,  would  destroy 
the  vitality  of  the  yeast ;  and  that,  notwithstanding  this  treat- 
ment, the  yeast  will  act  as  a  ferment. 
M.  Pasteur's  results,  however,  show  that  it  is  not  the  globules 
which  exercise  the  most  important  function  in  fermentation,  but 
the  conversion  of  the  soluble  portion  of  the  yeast  into  organized 
globules ;  for  he  shows  that,  when  the  globules  are  abstracted, 
the  ultimate  effect  produced  upon  the  sugar  is  essentially  the 
same  as  when  they  are  present.  Therefore,  it  is  certainly  of 
little  consequence,  whether  the  globules  are  abstracted  by  filtra- 
tion, as  in  M.  Pasteur's  experiment;  or  whether,  when  left 
mixed  with  the  soluble  portion,  their  vitality  is  destroyed  by  ex- 
posure to  a  temperature  of  212°  F.,  as  in  using  yeast  that  has 
been  dried  at  that  temperature,  or  boiled  with  water.  The 
