Ii6         Refined  Methods  in  Water  Purification.  {Km^^™m' 
The  Brandyvvine  water  is  an  extremely  polluted  stream,  receiving 
the  sewage  from  Coatesville  and  other  places.  The  water  in  the 
reservoir  receives  but  little  sedimentation  and  is  drawn  near  the 
bottom.  We  would  expect,  then,  that  the  water  from  the  reservoir 
would  contain  more  saprophytic  bacteria,  while  the  race-water  would 
contain  more  sewage  organisms.  This  is  admirably  demonstrated 
by  the  above  examinations.  Yet,  were  we  to  depend  on  the  bacte- 
rial count  on  gelatin  alone,  the  reservoir-water  would  appear  many 
times  worse  than  the  race-water.  It  is  thus  seen  that  by  the  proper 
combination  of  laboratory  methods  a  definite  and  accurate  conclusion 
may  be  reached,  and  it  is  also  evident  that  in  the  examination  of 
water  reliance  on  any  single  method  will  lead  to  grave  errors. 
SOME  REFINED  METHODS  IN  WATER  PURIFICATION. 
By  Wiuiam  G.  Topus. 
Two  years  ago  it  was  my  privilege  to  bring  to  the  attention  of 
this  body  some  observations  on  the  hygienic  purification  of  water. 
Since  then,  several  advances  in  technique  have  been  achieved  that 
serve  to  give  more  accurate  data  with  greater  economy  in  time. 
Bacteriological  investigation  directed  to  water  work  has,  in  the 
main,  a  different  end  from  that  which  is  sought,  ordinarily,  when 
applied  to  pathological  determinations.  The  latter  effort  seeks 
almost  wholly  to  isolate  and  identify  organisms,  where  with  water 
the  principal  study  is  to  determine  the  number  of  individual  organ- 
isms in  a  definite  volume  of  water,  regardless  of  their  kind  or  char- 
acter. The  assumption  being  that  an  impure  water  will  favor  the 
development  of  a  greater  number  of  organisms  than  a  water  with 
little  contamination,  since  organic  impurities  constitute  the  food 
supply  for  bacterial  growth.  That  this  is  a  fact  can  readily  be 
demonstrated  by  a  comparative  count,  on  equal  quantities  of  sewage 
and  any  potable  water.  Therefore,  in  this  line  of  investigation  the 
determination  of  numbers  becomes  the  principal  work,  and  much 
energy  has  been  directed  to  perfecting  methods  and  media  calcu- 
lated to  develop  the  greatest  numbers  of  organisms  contained  in  the 
water  under  examination.  But  while  this  is  the  principal  effort  in 
the  sense  of  having  more  time  devoted  to  its  study,  it  does  not 
monopolize  the  whole  importance.  It  is  necessary  that  a  frequent 
search  should  be  made  for  a  certain  organism  of  the  commensal 
