332 
ON  SOME  PROPERTIES  OF  FORMIC  ACID. 
from  ammonia  and  nitric  acid  ;*  but  they  cannot,  as  animals, 
assimilate  carbon,  unless  it  is  offered  in  the  state  of  a  ternary 
compound. 
It  is  now  four  years  since  I  proposed  fixing  the  limit  of  the 
synthetic  power  of  these  beings — that  is  to  say,  to  find  out  which 
was  the  most  simple  ternary  body  which  could  furnish  them  with 
assimilable  carbon.  Experiments  have  shown  that  nearly  all 
ternary  compounds  of  vegetable  or  animal  origin,  sugars,  tar- 
taric, succinic,  acetic,  oxalic,  &c,  &c.  acids,  can  each  separately, 
by  its  association  with  ammonia,  phosphoric  acid,  potash,  &c, 
form  mycogenic  media,  in  which,  under  certain  conditions, 
organized  productions  will  develop,  at  the  expense  of  the 
ternary  compound.  Formic  acid  forms  the  sole  exception,  and 
for  that  reason  merits  a  special  study,  which  I  have  but  recently 
been  able  to  undertake. 
I  first  proved  afresh  that  formic  acid,  free,  or  neutralised  by 
an  alkaline  or  earthy  base,  associated  with  the  mineral  elements 
P05,  NH3,  KO,  &c,  cannot  produce  a  mycogenic  liquid.  I 
have  kept  similar  preparations  for  more  than  six  months,  with- 
out the  appearance  of  the  least  organized  production  altering 
the  perfect  limpidity  or  the  chemical  composition  of  the  liquid. 
In  this  respect  formic  acid  differs  from  all  other  ternary  acids, 
including  oxalic  acid,  which,  under  these  conditions,  when  the 
solutions  are  not  too  much  concentrated,  and  their  acidity 
sufficiently  attenuated  by  the  addition  of  a  base,  will  give 
organized  productions. 
These  first  experiments  seem  to  show  that  the  molecule  of 
formic  acid  was  incapable  of  furnishing  carbon  assimilable  to 
the  simplest  cellular  organisms.  I  wish  to  find  out  whether 
this  assimilation  could  not  take  place  indirectly,  as  by  attrac- 
tion, associating,  in  the  mycogenic  medium,  the  formic  molecule 
with  one  more  condensed,  for  instance  sugar. 
I  have,  then,  made  some  mixtures,  in  which  the  carburetted 
element,  instead  of  being,  as  before,  simply  formic  acid,  was  an 
association  of  nearly  equal  parts  of  sugar  and  formic  acid,  com- 
bined with  lime  or  an  alkali.  Similar  mixtures  have  been  found 
highly  mycogenic,  and  have  given  abundant  results.    By  sufli- 
*  As  regards  nitric  acid,  I  am  not  quite  decided  on  this  point. 
