Oct,  1,  1896.] 
Sui^plement  lo  the  “ Tropical  AgricuUaristy 
291 
reproduction.  The  bacteria  which  cause  fernien- 
tative  changes  in  milk  can  he  destroyed  or  at 
least  their  development  and  activity  can  be  stayed 
in  many  ways. 
Boracic  acid,  carbonate  of  soda  and  salti)etre 
are  all  used  as  milk  preservatives,  the  first  being 
the  most  effective.  These  agents  do  not  destroy 
fermentative  organisms,  but  only  check  their 
development. 
If  the  udders  of  the  cows  and  the  hand  of  the 
milker  are  clean,  if  the  milk  vessels  have  been 
thoroughly  washed  and  well  scalded,  if  the  cows 
are  milker!  in  a jnire  atmosphere  and  if  tiie  uddei'.s 
ai'e  not  inflamed  or  otlierwise  diseased,  it  is 
clear  that  the  danger  of  organisms  entering  tlie 
milk  is  minimized. 
But  fermentative  bacteria  always  e.xist  in  the 
air  and  it  is  practically  impossible  to  prevent  milk 
coming  in  contact  with  them ; thei’efore  other 
precautiens  to  prevent  fermentative  changes  are 
necessary. 
Heat  will  kill  all  organisms  in  milk.  If  tlie 
heat  ap])lied  is  high  enough,  milk  will  be  steri- 
lized. Boiling  will  kill  all  bacteria.  If  boiled 
milk  is  kept  out  of  contact  with  the  air  it 
Mill  kee])  indefinitely.  I’reserved  or  condensed 
milk  is  prepared  by  evaporating  milk  to  Mdiich 
sugar  has  been  added  until  tlie  mixture  ac- 
quires the  consistence  of  syrup.  Whilst  hot  it 
is  hermetically  sealed  in  tins  and  keeps  good 
for  years.  A liigli  temperature  kills  the  ferments 
of  milk,  a low  temperature,  interrupts  their  ac- 
tivity if  it  does  not  actually  destroy  them. 
.Milk,  kept  frozen,  will  keej)  good  for  months, 
whilst  a mean  temjieraturc  of  3.'5°  to  40°  H.  is 
sufficiently  low  to  keei>  it  good  for  days.  A 
maximum  day  temperature  of  oo°  F.  will  en- 
able milk  to  be  kept  good  sufficiently  long  to 
allow  all  the  fat  globules  to  rise  to  the  surface. 
Whilst  if  the  mean  day  temperature  is  70°  F. 
or  higher  the  lactic  ferment  is  so  active,  that 
lactic  acid  is  formed  in  sufficient  quantity  to 
curdle  the  ca.“ein  in  a very  short  time,  and  the 
curdling  entangles  the  butter  fat  globules  so  that 
they  cannot  rise  to  the  surface. 
“NITKAGIN,”  OR  THE  FSF  OF  PFKF 
CULTIVATION  OF  BACTERIA  FOR 
LEGUMINOUS  CROPS. 
llellriegell’s  celebrated  experiments  have  al- 
ready been  referred  to.  Briefly  to  recapitulate 
these  : in  the  course  of  his  experiments,  llellriegell 
found  that  the  assimilation  of  the  free  nitrogen 
of  the  atmo.sphere  was  concurrent  M'ith  the 
development  on  the  roots  of  certain  leguminous 
plants— of  nodules  wdiich  w'ere  subsequently  found 
to  contain  specific  micro-organisms  or  Bacteria  ; 
hut  that  when  these  were  absent,  growth  of  the 
plant  was  stunted,  and  assimilation  of  free 
nitrogen  did  not  take  place.  Further,  that 
development — of  the  nodules  could,  speaking 
generally,  be  induced  in  sterilised  sand  supplied 
with  purely  mineral  food,  but  containing  no 
nitrogen,  provided  there  were  then  added  to  it 
the  watery  extract  from  a fertile  soil ; but  that 
in  the  case  of  certain  plants,  e.  (/.  lupins,  the  ex- 
tract from  an  ordinary  fertile  soil  did  not  suffice, 
though  that  of  a soil  in  which  the  particular 
crop  ex})erimented  on  had  been  previously  grow- 
ing well  M’as  effectual  in  producing  development 
of  the  nodules  on  the  roots. 
Working  on  the  lines  thus  enunciated  by 
llellriegel,  Nobbe  carried  the  inquiry  a step  further, 
and  he  reasoned  from  the  observations  made, 
more  particularly  in  the  case  of  lupins,  that  it 
M'as  very  jirobable  that  each  plant  posses.sed  its 
particular  kind  of  nodule,  or,  rather,  that  the 
nodules  of  particular  plants  contained  bacteria 
peculiar  to  themselves,  and  that  hence  what  was 
necessary  ivas  to  seek  to  ensure  for  the  plant 
grown  the  pre.'ence  of  the  particular  organisms 
that  favoured  the  as.similiation  by  it  of  the  free 
nitrogen  contained  in  the  atrao.sphere. 
Nobbe  accordingly  started  from  the  other  side 
of  the  question,  and  taking  the  nodules  which 
he  found  on  particular  leguminous  plants,  he  set 
to  work  to  eliminate  the  specific  organisms  and 
to  obtain  them  in  a pure  state.  It  had  been 
known,  as  1 have  already  pointed  out,  that  the 
growth  of  certain  leguminous  plants  like  lupins, 
which  would  not  thrive  on  ordinary  fertile  soils, 
could  be  induced  by  mixing  with  the  soil  other 
soil  from  where  lupins,  for  e.xample  had  been 
growing  well. 
But  it  was  also  known  to  Nobbe  that  this  trans- 
ference of  soil,  besides  being  costly  and  incon- 
venient, had  disadvantages  connected  with  it, 
for  not  only  Mere  the  sx)ecific  organisms  that 
might  be  favourable  present,  but  there  might 
be  others  that  Mere  distinctly  unfavourable  or 
destructive;  M'hile  fungoid  diseases,  parasitic 
growth.',  and  other  elements  of  a nature  prejudi- 
cial to  the  development  of  the  plant  might  also  be 
simultaneously  imported.  He  sought,  therefore, 
to  avoid  this  by  obtaining,  in  the  pure  state,  the 
specific  organisms  M’hich  muxs  believed  to  act 
favourably  in  the  case  of  each  leguminous  crop, 
and  ap.ut  fiom  the  disadvantages  that  might  at- 
tend the  presence  of  unfavourable  elements. 
The  method  adopted  by  Nobbe  and  Hiltner  M'as 
that  known  as  “ pure  cultivation.”  The  contents 
of  the  particular  plants  M'ere  used  for  inoculat- 
ing, in  the  usual  M-ay,  a plate  of  specially  pre- 
pared gelatine,  and  the  organisms  M’ere  cultivated 
on  it.  A second  plate  M’as  inoculated  from  one  of 
the  colonies  so  formed,  and  the  organisms  again 
cultivated.  This  M’as  repeated  succes.sively  until, 
finally,  a ‘‘pm'e  cultivation  ” was  obtained  of  the 
organisms  believed  to  be  the  one  peculiar  to  the 
particular  jilant,  and  the  one  bv  means  of  Mdiich 
nodules  were  formed  and  the  plant  M'as  enabled 
to  assimilate  the  free  nitrogen  of  the  atmosphere. 
On  examining  mico'-oscopically  the  organisms 
sbtained  from  the  nodules  of  different  leguminous 
plants,  Nobbe  could  not,  however,  discover  any 
external  appearances  which  specially  characterized 
one  or  the  other,  or  wdiicli  distinguished  one 
from  another. 
Indeed,  up  to  the  present,  it  has  not  been 
possible  to  say,  as  the  result  of  microscopial 
examination,  that  a particular  organism  is  the 
one  particular  to  peas,  to  clover,  to  lucerne  or 
to  any  leguminous  plant.  8till,  seeing  it  was 
known  that  in  order  to  get  lupins  to  groM’n,  ino- 
culation M itli  a soil  on  M’hich  lupins  had  thriven 
was  necessarj’,  but  that  inoculation  with  soil 
where  peas,  for  instance,  had  grown,  w'as  not 
effectual,  Nobbe  was  led  to  conclude  that,  though 
there  might  be  no  external  differences  in  tli^ 
