I 
342  DIFFUSION  OF  GERMS,  ETC. 
bj  the  process  indicated  above.  The  mjcodermic  vegetation  is 
then  developed  in  less  than  a  day,  and,  what  is  particularly  re- 
markable, it  is  developed  in  the  dark  as  well  as  in  the  light. 
The  ordinary  law  does  not  govern  these  little  organisms,  for  they 
neither  give  out  oxygen  nor  absorb  free  carbonic  acid  ;  but  on 
the  contrary  they  disengage  carbonic  acid,  and  increase  by 
fixing  ammonia  and  phosphoric  acid.  The  germs  w^hich  produce 
these  marvellous  effects  are  not  uniformly  distributed  in  the  air ; 
thus  Pasteur,  making  comparative  experiments  with  one  and  the 
same  liquid  arranged  in  flasks  completely  deprived  of  air,  found 
that  the  air  from  the  celLars  of  the  Observatory  contained  only 
one-tenth  part  as  many  germs  as  the  air  from  the  court  of  that 
establishment;  and  that  the  air  contained  fewer  germs  in  pro- 
portion to  its  elevation  in  the  atmosphere.  This  chemist  has 
performed  comparative  experiments  in  the  mountains  of  Jura, 
at  an  altitude  of  800  metres,  and  in  the  Alps  at  Montanvert, 
(Savoy),  at  2000  metres  above  the  level  of  the  sea;  and  he  has 
proposed  to  take  the  air  from  a  much  greater  elevation  by  the 
aid  of  a  balloon. 
These  researches  present  an  interesting  field  to  the  naturalist. 
Pasteur  has  many  species  in  vegetation,  new  and  hitherto  un- 
known. By  varying  the  conditions,  it  will  doubtless  be  possible 
to  obtain  others,  as  Paul  Laurent  has  already  done  with  the 
infusoria,  in  a  work  of  which  we  shall  speak  further  on.  On 
the  occurrence  of  these  researches,  Boussingault  called  atten- 
tion to  a  fact  pointed  out  by  Bineau,  of  Lyons,  who,  while  ex- 
amining a  specimen  of  rain-water,  containing  nitrates  and  am- 
monia in  solution,  found  these  materials  disappearing  under  the 
influence  of  cryptogamic  vegetation.  In  reference  to  this  great 
question  of  the  assimilation  of  nitrogen,  we  would  refer  the 
reader,  who  wishes  to  understand  it  thoroughly,  to  the  valuable 
work  of  Boussingault,  just  published,  entitled,  '^Agronomic, 
tJiimie  Agricole  et  Pliysiologie.'' 
In  order  that  plants  may  be  developed  in  meteoric  waters, 
these  waters  should  be  found  in  the  condition  of  Pasteur's  liquids. 
It  is  known  that  rain-water  contains  assimilable  nitrogen  and 
also  salts  of  potash,  soda,  lime,  &c.,  but  it  has  heretofore  lacked 
the  indispensable  element,  phosphoric  acid,  which  had  never 
been  detected  in  rain-water.    This  chasm  in  the  series  of  fer- 
