Am.  Jour.  Pharm.") 
November,  1904.  / 
Theory  of  Indicators,  etc. 
523 
and  the  materials  examined  in  the  space  of  three  hours,  with  very- 
few  exceptions  the  phenolphthalein  end  point  gives  a  fairly  accurate 
estimate  of  the  total  available  hydrochloric  acid  present  in  the 
stomach,  either  in  a  free  state  or  combined  more  or  less  feebly  with 
proteids.  The  influence  exerted  by  phosphates  is  usually  small, 
and  may  be  allowed  for  by  making  a  separate  estimation  of  the 
quantity  present  according  to  a  method  suggested  by  the  writer  in 
a  previous  paper.  The  end  point  of  phloroglucinvanillin  drops 
used  on  a  warm  plate  gives  a  fairly  accurate  estimate  of  the  actual 
free  hydrochloric  acid.  The  range  of  titration  from  the  phloro- 
glucinvanillin end  point  to  that  of  phenolphthalein,  after  allowing 
for  the  influence  of  phosphates  and  traces  of  organic  acid  may  be 
said  to  be  a  function  of  the  basic  affinities  of  proteids  and  their 
decomposition  products  present  in  the  solution.  The  total  range 
and  the  end  points  of  intermediate  indicators  are  dependent  upon 
the  total  quantity  of  such  bodies  present  in  the  solution  and  the 
extent  of  their  hydrolysis  or  decomposition,  and  provided  compar- 
able conditions  of  experiment  are  employed  this  range  may  be  said 
to  be  fairly  proportionate  to  the  peptic  activity  of  the  mixture. 
Under  pathological  conditions,  where  hydrochloric  acid  is  absent 
or  diminished  in  quantity,  and  peptic  digestion  fails  to  take  its 
normal  course,  especially  where  organic  acids  have  been  produced 
under  the  influence  of  bacteria,  the  above  rules  are  no  longer 
applicable.  The  total  range  no  longer  bears  the  slightest  relation- 
ship to  the  titration  results;  chlorides  determined  gravimetrically 
are  found  to  be  far  below  the  phenolphthalein  end  point;  the 
nitrogen  present  in  "so-called  phosphotungstic  filtrate  rises  above  the 
normal,  which  is  from  20  to  25  per  cent,  of  the  total  nitrogen  in  a 
well-digested  mixture.  All  these  factors  point  to  the  abnormal 
breaking  down  of  proteids  beyond  the  point  normally  reached  in 
peptic  digestion  in  the  stomach,  presumably  under  the  influence  of 
bacterial  enzymes  functioning  in  a  neutral  solution  with  the  libera- 
tion of  additional  weak  basic  and  acid  groups,  as  the  result  of  the 
abnormal  hydrolysis. 
In  tryptic  digestion  due  allowance  must  be  made  for  the  influence 
of  a  known  quantity  of  sodium  carbonate,  which  may  be  estimated 
independently.  Both  the  acid  groups  of  this  body  are  capable  of 
exerting  an  influence  upon  Porrier's  blue,  whilst  only  one  affects 
phenolphthalein,  and  other  indicators,  such  as  alizarin  or  phloro- 
