226  Purification  of  Drinking  Water.  \Km'^i^&xm' 
may  be.  The  water  is  always  clean  and  inviting.  This  result  alone 
would  have  made  the  effort  worth  while,  but  in  addition  to  this, 
we  have  an  achievement  that  cannot  be  measured  nor  calculated ; 
it  is  simply  invaluable. 
The  water  supply  of  Philadelphia  is  drawn  from  two  sources : 
the  Delaware  and  Schuylkill  Rivers.  These  streams  and  their  tribu- 
taries traverse  the  most  populous  territory  of  this  State.  They  are 
subject  to  every  variety  of  contamination,  from  mine  refuse  to 
household  sewage  in  such  quantities  that  their  waters  are  but  dilute 
sewage  in  fact.  Bacterial  examination  shows  astonishing  numbers 
and  varieties.  Dr.  Abbott  informs  us  that  he  has  found  spirilla 
among  their  number;  that  none  is  the  spirillum  of  Asiatic  cholera 
is  perhaps  due  to  good  fortune  and  effective  quarantine.  Certainly 
we  have  been  wide  open  to  every  kind  of  scourge  possible.  That 
this  is  now  at  an  end  is  clearly  and  conclusively  shown  by  a  study 
of  the  typhoid  fever  statistics  both  before  and  subsequent  to  the 
introduction  of  filtered  water.  These  tables  are  very  voluminous 
and  would  take  too  much  time  to  go  over  them  in  detail,  yet  it 
would  be  very  interesting  to  cite  a  few  examples  beginning  with 
January  5,  1906. 
Number  of  Cases  per  100,000  Population 
Date.  Raw  Water.    Filtered  Water. 
January  5    10.66  1. 
January  12    1740  r. 
January  19    14.08  1. 
January  26    17.80  1. 
February  2   :   I9-5I  o. 
February  9    21.61  1. 
February  16    27.63  o. 
February  23    19-63  1. 
March  2   17.64  2. 
March  9   10.70  1. 
March  16    9.97  o. 
March  23    10.80  o. 
March  30    12.24  2. 
The  record  of  filtered  water  in  West  Philadelphia  as  a  whole  is 
very  remarkable.  Eliminating  the  cases  which  when  traced  are 
found  to  have  originated  elsewhere,  the  number  remaining  credited 
to  the  district  is  so  small  as  to  leave  doubt  as  to  typhoid  in  this 
city  being  caused  to  any  extent  by  anything  except  the  water  supply. 
The  indications  of  this  are  so  positive  that  when  on  one  occasion 
last  summer  two  or  three  cases  of  typhoid  appeared  close  together 
