n8  Refined  Methods  in  Water  Purification.  {Kmij£^m£m 
nomena  that  further  light  was  diligently  sought  for  more  positive 
means  of  identification  of  this  germ,  and  a  decided  advance  has  been 
made  in  a  modification  of  the  Smith  tube  reaction  described  by 
Irons  and  others. 
It  has  been  found  that  when  neutral  aniline  red  is  added  to  lactose 
bouillon  medium  in  the  Smith  tube  and  a  culture  of  the  colon  bacillus 
added,  after  twenty-four  hours'  cultivation  at  37^°  C,  a  charac- 
teristic color  reaction  is  caused  by  the  growth  of  the  organism.  The 
liquid  in  the  stem  of  the  tube  assumes  a  decidedly  canary  color  with 
fluorescence,  while  that  portion  of  the  medium  remaining  in  the 
tube  retains  its  original  bright  red  color.  If,  then,  all  of  the  results 
appear,  namely,  the  volume  of  gas,  the  proper  percentages  of  it,  the 
acidity  and  the  typical  yellow-red  contrast  reaction,  then  the  organ- 
ism may  be  considered  Bacillus  coli  communis.  This  method  can 
be  carried  out  in  twenty-four  hours,  and  the  colon  bacillus  identified 
with  reasonable  certainty ;  whereas  the  same  result  with  isolation 
in  pure  culture  would  take  from  five  to  seven  days.  The  culture  to 
carry  out  this  experiment  may  be  selected  from  one  of  the  red 
colonies  grown  on  the  litmus  lactose  agar  plates  previously  described. 
The  science  of  bacteriology  is  so  new  and  its  application  to  water 
filtration  on  a  large  scale  so  recent  that  it  is  still  largely  in  the  experi- 
mental stage,  and  it  is  quite  natural  that  questions  should  be  con- 
tinually presenting  themselves  for  solution  in  every  branch  of  the 
work.  One  such  problem  is  of  interest,  and  it  involves  my  personal 
experience.  It  concerns  the  preservation  of  the  plates  from  prema- 
ture destruction  by  growths  c  certain  liquefying  organisms,  too 
irequently  found  in  river  water.  As  previously  stated,  no  pains 
have  been  spared  in  devising  media  calculated  to  coax  into  active 
growth  all,  or  as  many  as  possible,  of  the  organisms  contained  in 
the  water  under  examination.  Wide  experience  has  shown  that 
nutrient  gelatin  medium  fills  most  requirements  better  than  any 
other,  but  it  falls  down  in  one  respect,  at  least.  There  is  always 
present  a  class  of  germs  in  river  water,  called  liquefying  organisms. 
During  their  life  process,  they  excrete  a  principle  known  as  an 
enzyme.  This  substance,  in  many  cases,  is  exceedingly  active,  so 
great  at  times  as  to  digest  and  completely  liquefy  the  entire  con- 
tents of  a  plate  before  its  time  for  incubation  had  expired.  It  became 
necessary  to  prevent  the  very  Irequent  appearance  of  the  word 
"  lost  "  in  the  report,  and,  alter  some  experimenting,  the  problem 
