98  Analysis  of  the  Gastric  Contents.     { AFeif wTfs™- 
The  test  for  acetic  acid  is  as  follows  :  10  c.c.  of  the  contents  are 
shaken  with  50  c.c.  of  ether,  the  ether  drawn  off  and  evaporated, 
and  the  residue  dissolved  in  water.  This  aqueous  solution  of  the 
ethereal  extract  is  neutralized  with  sodic-hydrate,  and  a  few  drops 
Of  10  per  cent,  neutral  ferric  chloride  added.  If  acetic  acid  be 
present,  a  deep  red  color  results.  The  acid  may  also  be  discovered 
by  heating  the  contents  with  alcohol  and  sulphuric  acid  ;  the  ethyl 
ester  is  formed,  which  can  be  recognized  by  the  odor.  When  acetic 
acid  is  present  in  pathological  amount,  it  can  be  recognized  in  the 
odor  of  the  contents. 
SUMMARY. 
In  summary,  the  chemical  analysis  of  the  gastric  contents  is  con- 
ducted as  follows: 
(1)  Reaction  tested  with  litmus. 
(2)  Free  acid  is  tested  for  Congo  red. 
(3)  Test  for  free  HC1  with  phloroglucin-vanillin.  If  negative  or 
doubtful  with  this  reagent,  test  with  Boas  reagent,  00  tropeolin, 
Topfer's  reagent. 
(4)  Test  for  lactic  acid,  De  Jong  method. 
(5)  Test  for  butyric  acid. 
(6)  Test  for  acetic  acid. 
(7)  Measure  off  10  c.c.  of  the  mixed  contents  ;  to  this  add  2  to  3 
drops  of  phenothalein.  To  this  mixture  add  decinormal  soda-solu- 
tion from  a  burette,  testing  a  drop  of  mixture  for  free  HC1  by  phloro- 
glucin-vanillin after  each  addition  of  the  soda.  When  a  drop  fails  to 
give  the  Gunzberg  test,  record  the  reading  of  the  decinormal  solution 
present  when  the  test  was  last  obtained  for  the  reading  for  total  free 
HC1.  Continue  to  add  the  decinormal  solution  to  the  same  mixture, 
testing  a  drop  after  each  addition  with  Congo-red  paper  for  free  acids 
and  acid  salts.  Note  the  reading  when  the  Congo  red  ceases  to 
give  even  a  slight  brown  color.  At  this  point  test  a  drop  of  the 
mixture  with  a  drop  of  per  cent,  aqueous  solution  of  alizarin. 
Continue  adding  the  decinormal  solution  until  a  drop  of  mixture 
gives  a  pinkish-purple  color  with  alizarin.  Take  the  reading  for  the 
estimation  of  the  total  free  acids  and  acid  salts  (B). 
Where  this  alizarin  test  works,  it  is  to  be  used  as  the  index  of 
these  substances,  the  Congo  test  being  simply  an  adjuvatant  test. 
The  alizarin  test  is,  as  a  rule,  from  ^  to  ^  of  a  cubic  centimetre 
