344  RESEARCHES  ON  ACETIC  FERMENTATION. 
While  alcohol  is  present  the  small  vegetable  produces  acetic 
acid  ;  but  what  happens  if  the  alcohol  is  wanting  ?  M.  Pasteur 
shows  that  the  vegetable  can  in  this  case  bring  its  burning  action 
to  bear  on  the  acetic  acid  itself,  and  reduce  it  to  the  state  of 
water  and  carbonic  acid.  This  effect  seems  to  be  produced  only 
when  no  alcohol  is  present,  when  there  is  alcohol  the  combustion 
is  effected  by  preference  on  it. 
Such  is  the  action  of  the  mycoderm  under  the  ordinary  condi- 
tions ;  but  it  sometimes  alters,  and  having  no  longer  the  same 
appearance  or  the  same  consistence,  its  action  is  different.  It  is 
then  incapable  of  effecting  the  combustion  of  the  alcohol  to  the 
acetic  stage,  and  gives  intermediary  products  with  a  suffocating 
odor,  and  causing  the  eyes  to  water,  and  which  have  already  been 
obtained  in  the  oxidation  of  alcohol  and  ether  by  platinum  black. 
This  black,  under  other  conditions,  will  give  acetic  acid,  and  here 
between  platinum  black  and  mycoderma  vini  there  is  a  resem- 
blance of  effects  from  which  it  would  be  unsafe  to  infer  a  resem- 
blance of  causes.  The  only  inference  to  be  drawn  is  that  both 
are  means  of  transporting  the  oxygen  of  the  air  on  to  certain 
combustible  matters. 
For  the  production  of  acetification  it  is  necessary  that  the  my- 
coderm should  be  at  the  surface  of  the  liquid  :  the  process  is  ar- 
rested by  submersion,  and  only  recommences  on  the  formation  of 
a  fresh  film  on  the  surface. 
The  absorption  of  oxygen  by  this  film  is  complete,  and  not  a 
trace  of  this  gas  enters  the  liquid  through  it.  When  there  is,  as 
in  Orleans'  vinegar,  a  large  quantity  of  small  eels — animalculi 
needing  air  to  support  life — a  curious  contest  takes  place  between 
them  and  the  mycoderm,  the  latter  tending  to  engross  the  whole 
of  the  surface,  while  the  former  combine  all  their  efforts  to  sub- 
merge it  and  expose  the  liquid  in  which  they  live  to  free  contact 
with  the  air. 
The  complete  study  of  the  manner  in  which  this  ferment  acts 
and  of  the  last  interesting  particulars  will,  perhaps,  cause  some 
progress  to  be  made  in  the  industrial  preparation  of  vinegar  ;  but 
the  study  of  possible  improvements  must  be  left  to  the  manufac- 
turers.— Annates  de  VEcole  Normale,  i.,  from  Lond.  Chem.News, 
Jufylb,  1865. 
