Xvember'm-}  Theory  of  Indicators,  etc.  5 1 1 
ity  of  the  people  there  are  too  poor  to  afford  an  abundance  of  ice, 
and  must  buy  considerable  food  that  will  keep  without  it.  If  the 
commissioner's  methods  continue  till  the  next  census  is  taken, 
I  will  watch  with  extreme  interest  to  see  if  the  results  agree  with 
those  of  the  last. 
THE  THEORY -OF  INDICATORS  AND  ITS  BEARING  ON 
THE  ANALYSIS  OF  PHYSIOLOGICAL  SOLUTIONS 
BY  MEANS  OF  VOLUMETRIC  METHODS. 
By  G.  H.  A.  CXowes,  Ph.D. 
Gratwick  Research  Laboratory,  University  of  Buffalo. 
{Continued from  p.  467.) 
VI.  USE  OF  INDICATORS  IN  TITRATION  OF  NORMAL  STOMACH  CONTENTS. 
From  the  results  recorded  above,  bearing  in  mind  the  fact  that 
the  end  point  of  an  indicator  is  dependent  entirely  upon  the  state  of 
equilibrium  of  the  substances  present  in  the  solution,  it  must  be 
concluded  that  the  differences  observed  between  the  different  types 
of  indicators  in  conjunction  with  normal  stomach  contents  is  attribu- 
table, in  the  first  place,  to  the  nature  and  quantity  of  nitrogenous 
bodies  present.  In  other  words,  whilst  the  absolute  end  point 
obtained  with  any  given  indicator  may  be  a  function  of  the  acid  or 
acids  present,  the  range  from  the  lowest  end  point,  phloroglucinva- 
nillin  drops,  for  example,  to  the  highest,  phenolphthalein  or  Por- 
rier's  blue,  for  example,  is  almost  entirely  dependent,  in  the  first 
place,  upon  the  amount  of  nitrogenous  bodies  present,  and  in  the 
second  place  upon  the  extent  to  which  the  bodies  in  question  have 
been  hydrolyzed  with  the  liberation  of  basic  groups  capable  of  com- 
bining with  hydrochloric  or  other  acids  to  form  weak  salts.  Each 
individual  period  between  indicators  may  be  attributed  more  or  less 
to  the  influence  of  varying  types  of  amine  groups;  from  those 
which  in  virtue  of  their  union  with  carbon,  to  which  only  hydrogen 
is  bound,  may  be  looked  upon  as  extremely  positive,  to  those  lying 
in  close  proximity  or  directly  attached  to  a  CO  group,  which 
possess,  according  to  their  position  in  the  molecule,  either  very 
slight  positive  or  even  neutral  to  negative  characteristics.  It  cannot 
