32  Contamination  of  Drinking  Water.     {A £yPSm- 
causes  the  water  to  circulate  and  a  good  supply  of  air  and  nitrates 
is  obtained,  the  growth  is  most  luxuriant.  Thus  it  is  seen  that  tem- 
perature is  only  an  indirect  cause,  and  not  one  that  need  be  taken 
into  account  by  itself. 
The  class  Syngeneticeae  comprises  a  number  of  organisms  which 
until  recently  have  been  considered  animals.  Some  of  them  are 
certainly  plants  according  to  present-day  standards,  and  others  are 
so  near  the  line  separating  the  two  kingdoms,  that  botanists  are 
beginning  to  study  these  forms  quite  as  much  as  zoologists.  There 
is  a  single  member  of  this  class  which  probably  causes  more  trouble 
in  water  supplies  than  any  other  organism,  either  plant  or  animal. 
This  form,  known  as  Uroglena,  is  frequently  found  in  New  Eng- 
land, and  has  been  reported  as  far  west  as  Indiana.  The  proba- 
bilities are  that  it  is  widely  distributed  in  this  country,  but  has  not 
yet  been  recognized  in  many  localities.  In  appearance  Uroglena 
resembles  a  colorless  sphere  with  numerous  small  greenish  cells 
embedded  in  its  periphery.  The  whole  colony  may  become  almost  a 
half  millimetre  in  diameter,  although  it  is  usually  much  smaller.  The 
individual  cells  are  each  provided  with  a  pair  of  cilia  of  unequal 
length,  and  it  is  by  the  vibration  of  these  that  the  whole  colony  is 
revolved  through  the  water.  Each  cell  of  the  colony  contains  a 
nucleus,  a  red  spot  and  a  single  greenish  color  body,  besides  several 
vacuoles.  In  addition,  there  is  a  considerable  number  of  oil-globules, 
and  it  is  the  liberation  of  this  oil  which  causes  the  fishy,  oily  taste 
and  odor  produced  by  Uroglena.  Among  the  algae  and  Schizophy- 
ceae  the  contamination  is  nearly  always  brought  about  by  decay,  but 
in  this  case  the  trouble  is  produced  simply  through  the  mechanical 
breaking  up  of  the  organism  and  the  consequent  liberation  of  the 
oil  contained  within  the  cells.  Usually  the  pumping  or  gravity 
necessary  to  distribute  the  water  is  sufficient  to  free  the  oil,  for  the 
cells  are  very  fragile.  In  one  instance,  where  the  water  was  used 
almost  continuously  for  several  days  for  washing  caterpillars  off  the 
trees,  a  marked  increase  in  the  disagreeable  odor  and  taste  was  the 
result.  The  exact  nature  of  this  oil  is  not  very  well  understood. 
Calkins,  who  isolated  and  concentrated  it,  believed  it  to  be  similar 
to  the  essential  oils.  It  was  non- volatile  at  the  temperature  of  boil- 
ing water,  and  seemed  to  resemble  the  oils  obtained  from  diatoms 
and  the  blue-green  forms. 
No  sexual  method  of  reproduction  has  as  yet  been  observed 
