332 
ON  FERMENTATION. 
pure  sugar,  is  one  of  the  facts  most  important  in  relation  to  the 
theory  of  Professor  Liebig,  who  remarks  in  reference  to  it,  that 
"  if  the  fermentation  were  a  consequence  of  the  developement 
and  multiplication  of  the  globules,  they  would  not  excite  fermen- 
tation in  a  solution  of  pure  sugar,  which  is  destitute  of  other 
conditions  essential  for  the  manifestation  of  vital  activity  ;  this 
liquid  containing  no  nitrogenous  substance  necessary  for  the 
production  of  the  nitrogenous  portion  of  the  globules." 
It  cannot  be  denied  that  if  well  washed  beer-yeast  placed  in 
contact  with  a  solution  of  pure  sugar,  undergoes  alteration,  and 
is  destroyed,  there  can  be  no  possibility  of  pretending  that  alco- 
holic fermentation  is  a  phenomenon  correlative  with  the  devel- 
opement of  the  globules. 
But  M.  Pasteur  goes  on  to  show  that  the  facts  upon  which 
Prof.  Liebig  bases  his  argument  do  not  possess  that  degree  of 
exactitude  which  has  been  ascribed  to  them ;  and  also  that,  in 
the  fermentation  of  a  solution  of  pure  sugar,  there  is  an  amount 
of  vitality  and  organization  equal  to  that  manifested  in  the  more 
ordinary  case. 
With  the  object  of  illustrating  this  experimentally,  he  took 
two  equal  quantities  of  fresh  beer-yeast  that  had  been  washed 
with  a  large  quantity  of  water,  and  placed  one  in  contact  with 
a  solution  of  pure  sugar.  From  the  other  portion,  the  whole  of 
the  soluble  substance  was  extracted,  by  digesting  it  for  some  time 
with  a  large  quantity  of  boiling  water ;  the  globules  were  sepa- 
rated by  filtration ;  the  clear  liquid  mixed  with  sugar,  as  in  the 
other  experiments ;  and  so  small  a  quantity  of  the  fresh  yeast 
added  as  would  not  interfere  with  the  results  of  the  experiment. 
The  globules  increased,  the  liquid  became  turbid,  a  sediment  of 
yeast  was  gradually  deposited,  and  meanwhile  the  sugar  was 
transformed.  These  results  might  easily  have  been  anticipated ; 
but  there  is  another  fact  which  M.  Pasteur  points  out  as  import- 
ant to  be  considered.  In  determining  by  this  artifice,  the  con- 
version of  the  soluble  portion  of  yeast  into  organized  globules, 
a  considerable  quantity  of  sugar  is  decomposed.  In  one  instance, 
5  grammes  of  yeast  effected  the  decomposition  of  12.9  grammes 
of  sugar  within  six  days,  and  was  then  exhausted.  The  soluble 
portion  of  5  grammes  of  this  yeast  effected  the  decomposition 
