34  Contamination  of  Drinking  Water.     {A  j^S-fim110* 
single  remedy  that  would  prevent  or  remove  all  the  unpleasant 
effects  caused  by  these  organisms.  Each  form  must  be  studied  by 
itself,  and  it  is  only  after  all  the  information  possible  has  been  ob- 
tained with  regard  to  its  life  history  and  conditions  necessary  for 
growth  that  we  can  hope  to  prevent  or  exterminate  it.  Large 
quantities  of  statistics  are  available,  showing  the  kind  and  extent  of 
the  organisms  most  likely  to  occur  in  water  supplies,  and  we  have 
some  little  information  with  regard  to  the  climatic  conditions  which 
are  most  conducive  to  their  rapid  growth;  but  there  is  still  wanting 
a  great  many  details  which  can  only  be  obtained  from  patiently  cul- 
tivating these  plants  in  the  laboratory.  On  the  other  hand,  certain 
general  precautions  can  be  taken,  such  as  removing  the  top  soil  in 
making  new  reservoirs  and  storing  ground  water  in  the  dark,  which 
undoubtedly  prevents  the  introduction  and  growth  of  many  of  the 
most  troublesome  forms,  and  wherever  it  has  been  possible  to  apply 
these  methods  the  result  has  justified  the  expense.  It  is  certain 
that  it  is  just  as  necessary  to  have  a  thorough  microscopical  exami- 
nation of  a  water  supply  as  it  is  to  have  a  chemical  analysis,  and 
usually  the  most  practical  application  of  the  knowledge  thus  ob 
tained  can  be  made.  In  some  cases,  where  the  cause  of  pollution 
has  been  shown  to  be  due  to  some  plant  living  in  the  water,  it  has 
been  possible  to  cutout  that  part  of  the  supply  until  after  the  cause 
has  disappeared.  Again,  the  immediate  detection  of  obnoxious 
forms  often  permits  of  their  removal  before  decay  and  pollution 
take  place.  As  soon  as  people  understand  that  something  more 
than  a  mere  analysis  by  a  chemist  or  an  inoculation  of  guinea-pigs 
is  necessary  before  the  purity  of  a  water  supply  can  be  ascertained, 
there  will  be  a  greater  demand  for  those  who  can  make  accurate 
microscopical  examinations,  and  we  may  hope  for  an  increase  in  our 
knowledge  of  this  most  important  aspect  of  a  most  important 
subject. 
Direct  references  to  the  literature  were  impracticable  throughout 
the  foregoing,  but  a  short  bibliography  is  appended  for  the  benefit  of 
those  who  may  wish  to  get  more  specific  knowledge  of  the  points 
referred  to. 
GENERAL. 
Calkins,  G.  N.    The  Microscopical  Examination  of  Water.  23d 
Ann.  Rep.  of  Mass.  St.  Bd.  of  Health.  1891. 
