334 
ON  FERMENTATION* 
globules  collected  by  filtration,  after  having  been  exposed  to  a 
temperature  of  212°  F.,  are  almost  entirely  incapable  of  exciting 
fermentation. 
But,  it  may  be  asked,  why  does  the  fermentation  of  sugar  take 
place  under  the  influence  of  yeast  that  has  been  heated  to  212° 
F.,  if  that  fermentation  is  only  due  to  the  conversion  of  the  solu- 
ble portion  of  yeast  into  organized  globules,  seeing  that  such 
treatment  would  have  the  effect  of  destroying  the  vitality  of  the 
globules  ?  With  regard  to  this  point,  M.  Pasteur  believes  that 
fermentation  is  commenced  in  such  a  case,  in  the  same  manner 
that  it  sets  in  with  any  saccharine  liquid — such  as  grape  juice, 
sugar-cane  juice,  &c— that  is  to  say,  spontaneously ;  and  he 
believes  that  to  this  mode  of  origin  is  to  be  ascribed  the  retarda- 
tion, characteristic  of  fermentation  produced  by  yeast  that  has 
been  dried  at  212°  F.,  as  well  as  its  longer  duration  in  this  case. 
Hence  it  would  appear  that  in  all  cases,  even  those  which  might 
be  regarded  as  furnishing  the  chief  support  of  the  opinion  that 
organization  does  not  exercise  any  casual  influence  on  the  phe- 
nomena of  fermentation,  the  chemical  change  by  which  they  are 
characterized  is  always  correlative  with  the  gradual  and  progres- 
sive formation  of  the  organized  globules. 
M.  Pasteur  has  also  made  some  further  observations,  which 
confirm  the  results  described  already,  and  also  throw  a  new  light 
on  the  subject  of  fermentation.  The  existing  theory  sets  out 
from  the  assumption  that  the  ferment  does  not  contribute  any- 
thing to,  or  abstract  anything  from  the  fermenting  substance. 
M.  Pasteur,  however,  endeavors  to  show  that  this  is  not  a  cor- 
rect representation  of  the  fact,  but  that  the  yeast  does  abstract 
substance  from  the  sugar,  that  the  sugar  is  one  of  its  aliments, 
and  that  there  is  not  a  chemical  equivalence  between  the  quanti- 
ties of  alcohol,  and  carbonic  acid  (lactic  acid,)  on  the  one  hand, 
and  the  quantity  of  sugar  fermented  on  the  other. 
For  the  purpose  of  illustrating  these  facts  he  took  two  equal 
portions  of  well  washed  fresh  yeast,  dried  one  in  a  capsule,  and 
ascertained  the  weight  at  212°  F.  This  weight  would  in  any 
case  be  inferior  to  that  of  the  other  portion,  also  dried  at  212° 
F.,  and  collected  only  after  it  had  been  exhausted  in  the  presence 
of  an  excess  of  sugar.  The  difference  of  weight  was  found  to 
be  variable,  but  it  was  always  very  sensible.    It  must  be  stated 
