﻿CHAPTER 
  XIV 
  

   THE 
  BACTERIA 
  

  

  186. 
  What 
  are 
  the 
  bacteria? 
  When 
  a 
  dish 
  of 
  water 
  in 
  

   which 
  cut 
  flowers 
  have 
  been 
  kept 
  for 
  several 
  days 
  is 
  carefully 
  

   examined, 
  a 
  thin 
  film, 
  or 
  scum, 
  may 
  often 
  be 
  found 
  on 
  the 
  sur- 
  

   face 
  of 
  the 
  water. 
  This 
  surface 
  film 
  usually 
  consists 
  of 
  many 
  

   millions 
  of 
  bacteria. 
  The 
  bacteria 
  have 
  thrived 
  upon 
  the 
  plant 
  

   substances 
  which 
  were 
  dissolved 
  in 
  the 
  water. 
  The 
  bacteria 
  

   also 
  produce 
  the 
  unpleasant 
  odors 
  that 
  often 
  arise 
  from 
  such 
  

   a 
  dish 
  of 
  cut 
  flowers. 
  If 
  but 
  a 
  few 
  bacteria 
  had 
  gathered 
  at 
  

   the 
  water's 
  surface, 
  they 
  could 
  not 
  be 
  seen 
  except 
  by 
  the 
  use 
  

   of 
  very 
  great 
  magnification, 
  but 
  when 
  such 
  large 
  numbers 
  

   accumulate 
  in 
  one 
  place, 
  they 
  may 
  easily 
  be 
  seen, 
  just 
  as 
  it 
  is 
  

   easier 
  to 
  see 
  a 
  pile 
  of 
  sand 
  than 
  it 
  is 
  to 
  see 
  a 
  few 
  grains 
  of 
  sand. 
  

  

  The 
  bacteria 
  are 
  extremely 
  simple 
  one-celled 
  plants. 
  The 
  

   fact 
  that 
  they 
  are 
  plants 
  was 
  not 
  generally 
  recognized 
  until 
  

   within 
  the 
  past 
  few 
  decades. 
  Although 
  this 
  group 
  of 
  plants 
  

   is 
  still 
  imperfectly 
  known, 
  much 
  has 
  been 
  learned 
  of 
  then 
  1 
  very 
  

   great 
  hygienic 
  importance. 
  It 
  has 
  been 
  popularly 
  supposed 
  

   that 
  all 
  or 
  nearly 
  all 
  of 
  the 
  bacteria 
  are 
  causes 
  of 
  disease, 
  

   although 
  it 
  is 
  now 
  believed 
  by 
  scientists 
  that 
  very 
  few 
  of 
  

   them 
  are 
  disease-producing. 
  On 
  the 
  other 
  hand, 
  there 
  are 
  

   many 
  kinds 
  of 
  bacteria 
  that 
  live 
  in 
  such 
  ways 
  as 
  greatly 
  to 
  

   aid 
  in 
  important 
  processes 
  upon 
  which 
  men 
  depend. 
  

  

  187. 
  The 
  size 
  and 
  structure 
  of 
  the 
  bacteria. 
  The 
  bacteria 
  

   are 
  so 
  small, 
  and 
  there 
  are 
  so 
  many 
  kinds 
  of 
  them, 
  1 
  that 
  it 
  is 
  

   not 
  easy 
  to 
  give 
  a 
  clear 
  answer 
  to 
  the 
  question 
  as 
  to 
  what 
  

   they 
  are. 
  Indeed, 
  they 
  are 
  so 
  small 
  that 
  the 
  figures 
  given 
  for 
  

  

  1 
  It 
  has 
  been 
  estimated 
  by 
  Migula, 
  a 
  good 
  authority, 
  that 
  there 
  are 
  at 
  

   least 
  1272 
  distinct 
  species 
  of 
  bacteria. 
  

  

  199 
  

  

  