I  might  greatly  prolong  this  enumeration  ;  but
enough,  I  think,  has  been  adduced  to  justify  me  in
stating  that  Liebig,  like  Faraday,  merited  the  old
classical  encomium,  illustrans  commoda  vitce ;  and
never,  in  his  conscientious  benevolence,  lost  sight  of
the  general  interests  of  his  race.
It  was  not,  however,  incidentally  only,  by  the
collateral  development  of  the  industrial  arts,  that  the
practically  beneficent  outcome  of  Liebig's  genius
was  displayed.  In  fathoming  the  deep  mysteries  of
organic  chemistry,  his  penetrating  curiosity  could
not  remain  indifferent  to  the  yet  more  profound
secrets  of  biology,  that  is  to  say,  of  life,  in  its  two
great  forms,  vegetal  and  animal,  based,  as  they  both
are,  in  their  material  development,  on  processes  of
chemical  change.
In  the  laws  of  plant-life  more  especially,  Liebig's
noble  researches  threw  ray  after  ray  of  brilliant
light  into  depths  where  before  the  deepest  obscurity
had  reigned.  It  was  Liebig  who  traced  the  primor-
dial conditions  of  the  nutrition  and  growth  of  plants  ;
and  finally    established    their   connection    with   the


THE    FARADAY    LECTURE.  15

chemical  composition  of  the  soil  in  which  they  are
rooted,  and  of  the  air  in  which  their  leaves  are  bathed,
as  well  as  with  the  imponderable  forces,  especially
the  sun's  light  and  heat,  under  whose  influence  they
live.
Projecting  his  view  still  further  in  the  same
direction,  he  also  traced  the  influence  of  physical
and  chemical  laws  on  the  second  and  higher  division
of  biology,  namely,  that  which  relates  to  animal  life,
its  laws  and  conditions,  especially  those  of  the  nutri-
tion and  development  of  the  animal  body.
