36  Analysis  of  the  Gastric  Contents.      {A  januaryfS."1 
tions  of  hydrochloric  acid.  Where  the  acid  is  mixed  with  other 
substances,  particularly  with  organic  acids,  as  in  the  gastric  contents, 
this  equality  of  the  different  tests  does  not  hold.  In  cases  where 
considerable  amounts  of  organic  acid  are  present  it  is  impossible  to 
make  an  accurate  reading  from  the  Tbpfer  test.  In  other  cases, 
owing  to  conditions  not  thoroughly  understood,  the  Gunzburg  test 
will  react,while  the  00  Tropeolin  fails,  or  the  Tbpfer  test  works  where 
the  Boas  fails,  or  vice  versa.  It  is  my  custom  in  general  work  to 
depend  upon  all  four  reagents.  The  Gunzburg  test  I  have  found 
the  most  satisfactory  for  the  varying  conditions.  I  therefore  test  the 
contents  first  with  this  test.  If  it  reacts,  free  hydrochloric  acid  is 
present.  If  it  fails,  the  Boas,  Tbpfer  and  oo  Tropeolin  tests  are 
tried  in  turn.  It  is  only  when  a  positive  test  is  lacking  with  all  four 
that  free  hydrochloric  acid  is  recorded  absent. 
The  methods  for  the  quantitative  determination  of  the  hydro- 
chloric acid  are  of  several  kinds.  Three  type  methods  serve  to 
illustrate  the  different  principles  employed  in  the  various  methods  : 
(1)  Methods  based  upon  the  determination  of  the  total  hydro- 
chloric acid  by  precipitation  and  estimation  of  the  total  chlorine 
present. 
(2)  Methods  based  upon  the  determination  of  the  total  HC1  by 
estimation  of  the  acidity  of  the  ash. 
(3)  Methods  based  upon  the  determination  of  the  total  HC1  by 
the  reaction  of  color  reagents. 
The  precipitation  method  is  best  represented  by  the  method  of 
Martius  and  Luttke,  which  is  the  most  accurate  of  all  the  methods 
of  this  class.36  This  consists  of  the  estimation  of  the  total  hydro- 
chloric acid  by  determination  of  the  total  chlorine  of  the  ash  not 
present  in  the  form  of  chlorides.  This  method,  as  all  the  accu- 
rate methods  of  this  class,  is  too  difficult  for  clinical  work. 
The  second  type  of  method  is  represented  by  the  method  of  See- 
man.37  This  method  consists  of  (a)  the  neutralization  of  the  total 
acidity  of  the  contents  with  soda  solution,  in  known  amount ;  (b) 
the  reduction  of  the  contents  to  the  ash,  thereby  driving  off  all  the 
organic  compounds ;  {c)  the  estimation  by  titration  with  decinormal 
acid  solution  of  the  acidity  lost  by  this  reduction;  (d)  the  estima- 
tion of  the  total  hydrochloric  acid  by  subtraction  of  the  lost  organic 
36  Martius  u.  Luttke  :  Magensaured.  Menschen,  Stuttgart,  1892. 
3  7  Seeman  :  Zeitschr.  f.  klin.  Med.,  Bd.  V,  s.  273. 
