ON  SOME  PROPERTIES  OF  FORMIC  ACID.  333 
ciently  prolonging  the  experiment,  it  will  always  be  found  that 
a  more  or  less  considerable  portion  of  the  formic  acid  will  have 
disappeared  during  the  vegetation.  Sometimes  even,  it  will  have 
entirely  disappeared.  Is  this  disappearance  of  formic  acid  due 
to  true  assimilation  ?  or  to  a  phenomenon  of  extra- organic  oxida- 
tion, analogous  to  that  which  takes  place  during  the  acetification 
of  alcohol,  under  the  influence  of  the  formation  of  mother  of 
vinegar  ?  This  is  a  question  which  my  experiments  have  not 
yet  been  able  to  solve. 
I  have  in  the  above  italicised  the  word  "  combined,"  because, 
in  fact,  the  mixed  preparations  remain  perfectly  sterile  if  they 
contain  a  very  small  proportion  of  free  formic  acid.  I  have 
proved  that  a  thousandth  of  free  formic  acid  is  sufficient  to  keep 
solutions  of  sugar  from  altering,  though  very  mycogenic  without 
this  addition. 
This  property  is  remarkable.  I  ascertained  that  it  does  not 
depend  on  a  purely  chemical  action  by  establishing  a  comparison 
between  perfectly  similar  preparations,  except  that  the  formic 
acid  was  replaced  by  an  energetic  mineral  acid — hydrochloric 
acid — the  greatest  quantity  being  five  to  six  thousandths.  After 
a  certain  time  these  preparations  produced  mycoderms,  much 
less  rapidly,  it  is  true,  than  in  unacidulated  solutions. 
I  sought  another  comparison  in  phenic  acid  or  phenol,  and 
found  that  by  putting  side  by  side  mycogenic  sugared  prepara- 
tions, to  which  I  added  in  one  case  from  one  to  two  thousandths 
of  formic  acid,  and  in  the  other  an  equal  proportion  of  phenol, 
the  former  nearly  always  remained  unchanged. 
This  was  not  the  case  with  fresh  muscular  flesh.  Having 
placed  three  pieces  of  beef,  weighing  each  about  30  decigrammes, 
in  three  bottles  containing,  the  first  200  cubic  centimetres 
of  water  with  a  thousandth  of  phenic  acid,  the  second  200  cubic 
centimetres  of  water  and  a  thousandth  of  formic  acid,  the  flesh 
was  preserved  a  relatively  much  greater  time  than  that  of  the 
two  others ;  that  in  the  water  acidulated  bv  formic  acid 
putrefied  much  more  slowly  than  that  in  the  distilled  water  and 
presented  peculiar  phenomena.  Thus,  the  liquid  surface  was 
covered  with  a  thick  mycodermic  layer,  which  was  not  the  case 
with  the  two  others.    After  some  time  the  three  liquids  pre- 
