Am.  Jour.  Pharrn."! 
December,  1904.  S 
Purification  of  Water  Supplies. 
555 
voirs  are  carefully  constructed  and  the  majority  of  the  organic  mat- 
ter excluded  by  concreting  the  reservoir,  there  is  even  then  a  strong 
possibility  of  the  water  being  rendered  unfit  for  use  by  the  presence 
of  these  obnoxious  plants.  Filtered  water  is  more  subject  to  algal 
pollution  than  surface  water,  because  any  water  passing  through  a 
considerable  layer  of  sand  is  apt  to  pick  up  certain  nutrient  salts 
which  enable  the  water  to  sustain  algal  life  in  larger  proportions 
than  it  would  otherwise  do.  Still  another  method  supposed  to  pre- 
vent contamination  by  algae  is  that  of  pumping  air  into  the  water, 
or  aerating  it  by  means  of  some  sort  of  spraying  apparatus. 
Unfortunately,  however,  many  of  the  unicellular  algae  are  able  to 
multiply  more  rapidly  with  a  plentiful  supply  of  air  than  without  it, 
and  for  this  reason  aerated  water  has  been  known  to  give  rise  to 
serious  algal  growth  when  it  would  otherwise  have  been  unable  to 
sustain  the  life  of  these  plants  in  any  considerable  quantity.  In 
certain  parts  of  New  England  the  conditions  due  to  the  presence  of 
these  plants  are  notorious,  the  trouble  being  very  serious  and  the 
water  frequently  unfit  for  use  a  considerable  part  of  the  year.  But 
the  difficulty  is  by  no  means  confined  to  this  region,  there  being 
scarcely  a  State  in  the  Union  which  has  not  reported  serious  diffi- 
culties of  the  same  kind.  Since  the  condition  seemed  to  be  one 
which  called  for  some  relief  and  none  of  the  used  methods  were  of 
more  than  partial  benefit,  it  seemed  advisable  that  the  problem  be 
taken  up  from  an  entirely  new  standpoint,  and  for  this  reason  a 
series  of  investigations  were  undertaken  for  the  purpose  of  gather- 
ing all  the  information  possible  in  regard  to  the  life  history  of  the 
organisms,  as  well  as  the  physiological  effect  of  certain  substances 
under  laboratory  conditions.  A  large  number  of  substances  were 
experimented  with,  and  in  a  very  short  time  it  became  evident  that 
nothing  was  so  toxic  in  high  dilutions  to  these  forms  as  certain  of 
the  heavy  metals. 
At  about  this  time  an  opportunity  presented  itself  for  experiment- 
ing on  a  large  scale  in  the  cress  beds  of  the  South.  Here  the  con- 
ditions were  such  that  after  the  cress  had  been  cut  and  before  the 
new  growth  could  start,  a  thick  heavy  mat  of  algae  would  form 
over  the  surface  of  the  water  sufficient  to  prevent  the  growth,  if  not 
entirely  smother  out  the  delicate  cress  plants.  Since  water  cress  at 
that  time  of  the  year  was  worth  about  $20  a  barrel,  and  the  demand 
was  considerably  greater  than  the  supply,  a  large  amount  of  money 
