A  January^r*}      Analysis  of  the  Gastric  Contents.  39 
first  records  the  end  of  the  acid  reaction,  while  the  latter  records  the 
actual  alkaline  reaction. 
By  the  subtraction  of  the  total  acidity  due  to  free  acids  plus  acid 
salts  [b)  from  the  total  acidity  (a),  the  acidity  due  to  combined  acids 
is  obtained  (c).  Where  free  hydrochloric  acid  is  present,  all  of  the 
combined  acid  is  combined  hydrochloric  acid,  whatever  organic 
acids  may  be  present.42 
The  estimation  of  the  total  free  hydrochloric  acid  (d)  is  performed 
by  titration  with  the  decinormal  soda  solution  until  the  test  for  free 
HC1  can  no  longer  be  obtained.  Ten  cubic  centimetres  of  the  con- 
tents, to  which  two  drops  of  the  y2  per  cent,  alcoholic  solution  of 
di-methyl-amido-azo-benzol  have  been  added,  are  titrated  with  the 
soda  solution  until  the  red  color  of  the  mixture  gives  place  to  a  yel- 
low color.  This  point  determines  the  neutralization  of  the  free 
HC1.  This  is  the  simplest  method  of  performing  this  test.  It  has, 
however,  one  great  disadvantage  as  a  test  for  general  use.  Where 
any  considerable  quantity  of  organic  acids  is  present  in  the  con- 
tents, the  point  of  transition  from  a  carmine-red  to  a  yellow  color 
is  not  sharp  and  cannot  be  accurately  determined.43  The  organic 
acids  give  a  brownish-red  color,  which  is  not  unlike  the  much  diluted 
carmine  red  of  the  mineral  acids.44  For  this  reason  I  have  used 
phloroglucin-vanillin  as  the  indicator  in  place  of  or  in  addition  to 
Tbpfer's  reagent.  The  test  with  this  reagent  can  never  be  confused 
by  the  presence  of  organic  acids  or  other  constituents  of  the  gastric 
contents.  Ten  cubic  centimetres  of  the  contents  are  titrated  with 
the  soda  solution  until  a  drop  of  the  mixture  fails  to  give  the  free 
HC1  reaction  with  phloroglucin-vanillin.  The  last  reading  before 
the  failure  of  the  test  is  taken  as  the  measure  of  the  hydrochloric 
acid.  Thus,  if  the  test  responds  after  the  addition  of  4  c.c.  one- 
tenth  soda  solution  and  fails  with  the  addition  of  4-1  c.c,  the  free 
HC1  in  the  10  c.c.  of  contents  =  4  X  '00365  gramme. 
The  total  hydrochloric  acid  (e)  is  determined  by  the  addition  of  the 
total  combined  HC1  (c)  and  the  total  free  HC1  (d),  in  cases  where 
free  HC1  is  present.  Where  no  free  HC1  is  present  the  total  hydro- 
chloric acid  can  be  estimated  by  the  following  method  (Mintz 
method): 
42  Boas  :  Loc.  cit. 
43Hari:  Archiv  f.  Verdauungskrankheiten,  Bd.  II,  H.  203. 
44  Strauss  :  Deutsches  Archiv  f.  klin.  Med.,  Bd.  LXVI,  H.  1. 
Mohr  :  Loc.  cit. 
