26  Contamination  of  Drinking  Water.     {A  January j9oo.m' 
The  question  is  one  which  naturally  appeals  to  the  engineer,  and 
for  a  long  time  it  was  left  entirely  to  him  to  determine  not  only  how 
the  water  was  to  be  obtained  and  supplied,  but  also  its  quality. 
Too  often  the  quality  was  a  matter  that  was  given  little  or  no  con- 
sideration, and  topographical  or  financial  consideration  decided  in 
favor  of  a  supply  that  afterwards  proved  to  be  unfit  for  use,  if  not 
absolutely  dangerous.  Later,  the  chemist  was  called  in,  and,  while 
people  now  knew  just  the  amount  of  mineral  and  organic  matter 
contained  in  the  water  and  deductions  could  be  made  showing  that 
this  matter  probably  came  from  certain  sources,  there  was  still  no 
getting  at  the  actual  cause  of  a  great  deal  that  contaminated  water 
supplies  until  recourse  was  had  to  the  microscope.  It  is  quite  as 
necessary  to  determine  the  origin  and  condition  of  organic  matter 
found  in  water  as  to  know  the  exact  quantity  and  quality  of  it,  and 
in  many  cases  the  true  interpretation  of  a  chemical  analysis  depends 
entirely  upon  a  direct  biological  examination. 
The  history  of  the  microscopical  study  of  water  in  connection 
with  its  wholesomeness  is  one  which  extends  over  a  comparatively 
short  time  and,  until  quite  recently,  there  have  been  scarcely  any 
who  gave  their  whole  attention  to  this  aspect  of  the  subject.  It  is, 
however,  fast  becoming  recognized  as  most  important  and  neces- 
sary, and  the  public  are  coming  to  demand  that  the  water  they  use 
be  subjected  to  biological  examination  as  well  as  chemical  analysis. 
It  will,  perhaps,  be  profitable  to  consider  a  few  special  forms 
which  give  rise  to  disturbances  in  water  supplies,  and  to  point  out 
some  of  the  reasons  for  these  organisms  causing  pollution  and  un- 
wholesomeness. 
We  shall  confine  ourselves  to  a  group  of  plants  known  as  the 
algae,  which,  aside  from  the  bacteria,  produce  more  trouble  than  any 
other  members  of  the  vegetable  kingdom.  The  bacteria  are  recog- 
nized as  being  responsible  for  much  disease  and  discomfort,  although 
the  actual  number  which  prevent  the  same  is  vastly  in  the  majority. 
This  group  and  certain  animals  of  a  low  order  which  contaminate 
water  would  each  form  the  subject  of  an  entire  article,  and  for  this 
reason,  must  be  left  out  of  consideration  at  this  time. 
The  group  of  the  algse  contains  a  number  of  forms  which  are 
wonderfully  varied,  both  as  to  their  size  and  method  of  growth  ;  and, 
while  the  large  red  and  brown  "  sea-weeds  "  belong  to  this  class,  it 
is  the  grass-green  forms  which  are  most  often  found  in  fresh  water. 
