142  •      Purification  of  Drinking  Water.      { ^mMi£&  *m  m* 
the  copper  spigot  to  which  the  filter  was  attached.  That  the  inhib- 
iting action  of  the  filtered  water  was  due  to  its  contact  with  the 
copper  spigot  is  shown  by  the  fact  that  when  we  used  a  filter  in 
which  contact  with  copper  was  avoided,  the  typhoid  organisms  con- 
tinued to  grow  the  same  as  in  distilled  and  tap  water. 
Later  experiments  showed  that  contact  of  the  copper  foil  with  the 
water  for  a  very  brief  period  of  time  was  sufficient  to  affect  these 
organisms.  We  found,  for  instance,  that  if  the  copper  foil  were 
allowed  to  remain  in  distilled  water  for  one  to  five  minutes,  the 
typhoid  organisms  were  completely  destroyed  within  a  few  hours. 
In  a  paper  presented  to  the  American  Philosophical  Society,  the 
results  of  my  work  along  this  line  are  summarized  as  follows: 
Certain  intestinal  bacteria  like  colon  and  typhoid  are  completely 
destroyed  by  placing  clean  copper  foil  in  water  containing  them,  or 
by  adding  the  organisms  to  water  previously  in  contact  with  copper 
Foil. 
The  toxicity  of  water  to  which  either  copper  coins  or  copper  foil 
has  been  added  is  probably  due  to  a  solution  of  some  salt  of  copper, 
as  first  suggested  by  Naegeli. 
The  copper  is  probably  in  the  form  of  a  crystalloid  rather  than 
that  of  a  colloid,  as  it  has  the  property  of  permeating  the  cell  walls 
and  organized  cell  contents  of  both  animals  and  plants,  thereby  pro- 
ducing the  toxic  effects. 
While  the  effects  produced  by  the  oligodynamic  action  of  copper 
are  apparently  different  from  those  of  true  chemical  poisons,  the 
difference  is  probably  in  degree  only  and  not  in  kind. 
Certain  lower  organisms,  including  both  plants  and  animals,  pos- 
sess a  specific  sensitiveness  to  minute  quantities  of  copper,  and  it  has 
been  shown  that  they  are  not  restored  on  transferring  them  to  water 
free  from  oligodynamic  properties. 
Oligodynamic  solutions  of  copper  are  obtained  by  adding  either 
copper  coins,  copper  foil,  or  salts  of  copper  to  water ;  when  copper 
foil  is  used,  sufficient  copper  is  dissolved  by  the  distilled  water  in 
one  to  five  minutes  to  kill  the  typhoid  organisms  within  two  hours. 
A  solution  of  copper  may  lose  its  toxicity  by  the  precipitation  of 
the  copper  as  an  insoluble  salt  or  compound ;  by  its  absorption  by 
organic  substances  ;  or  by  adsorption  by  insoluble  substances. 
The  oligodynamic  |Ction  of  the  copper  is  dependent  upon  tem- 
perature, as  first  pointed  out  by  Israel  and  Klingmann. 
