AmAt§uiiPimm'}  S°me  Recent  Literature.  391 
of  the  problem,  and  see  what  results  would  be  yielded  by  making  a 
study  of  the  physiology  of  the  organisms  under  laboratory  condi- 
tions, the  object  being  to  discover  some  substance  which,  because  of 
its  toxic  action  on  the  algae,  would  prevent  their  growth  in  water 
supplies. 
In  determining  such  a  physiological  method  it  was  necessary  to 
consider  not  only  that  the  remedy  must  be  cheap  enough  for  prac- 
tical purposes  and  readily  available,  but  that  it  must  be  harmless  to 
man  under  the  conditions  used.  A  large  number  of  substances 
were  experimented  with,  but  copper  sulphate  gave  the  most  satis- 
factory results.  As  stated  by  the  writers,  "  this  salt  has  a  very 
high  toxicity  for  algae,  and  experiments  with  a  number  of  the  forms 
usually  found  in  reservoirs,  and  the  source  of  much  trouble,  have 
shown  that  inconceivably  small  amounts  of  copper  are  poisonous  in 
a  high  degree." 
In  the  method  proposed  the  death  points  of  the  algae  were  deter- 
mined by  using  Van  Tieghem  cells.  Accurate  solutions  were  made 
with  distilled  water  and  200  c.c.  of  each  solution  was  pipetted  into 
an  Erlenmeyer  flask.  The  algae,  if  filamentous  forms,  were  rinsed ; 
if  free-swimming,  they  were  concentrated  by  the  Sedgwick-Rafter1 
method  from  500  c.c.  volume  to  5  c.c.  volume,  and  this  was  added 
to  the  treated  water,  the  inaccuracy  due  to  this  addition  being  dis- 
regarded. At  the  same  time  control  experiments  were  also  car- 
ried on. 
The  species  tested  are  divided  into  three  groups,  as  follows:  (1) 
Those  with  death  points  at  higher  concentrations  than  I  part  copper 
sulphate  to  1,000,000  parts  of  water;  (2)  those  with  death  points 
between  1  to  1,000,000  and  1  to  5,000,000 ;  and  (3)  those  with  death 
points  at  greater  dilutions  than  1  to  5,000,000. 
Having  demonstrated  the  effectiveness  of  copper  sulphate  as  an 
agent  for  the  destruction  of  algae,  the  authors  discuss  the  effects  of 
copper  and  its  compounds  on  the  animal  economy,  and  arrive  at  the 
conclusion  that  "  even  if  the  maximum  concentration  of  copper 
sulphate  necessary  to  destroy  algae  in  reservoirs  were  maintained 
indefinitely,  the  total  absorption  from  daily  use  would  be  very  far 
below  an  amount  that  could  produce  the  least  unpleasant  effect."  In 
other  words,  taking  a  dilution  of  1  to  1,000,000,  which  would  in  all 
1  Whipple  :  "  The  Microscopy  of  Drinking  Water."    New  York,  1889,  p.  15. 
