42  Analysis  of  the  Gastric  Contents.  {A^S&f&rm' 
soda  solution  is  necessary  to  neutralize  the  acid  phosphates,  as  in 
the  absence  of  CaCl2 ;  hence  the  division  by  2  of  the  final  result. 
If  this  total  acid  salts  {G)  be  subtracted  from  the  total  of  organic 
acids  plus  acid  salts  obtained  as  described  above,  but  after  the  addi- 
tion of  5  c.c.  of  concentrated  solution  of  CaCl2  to  the  10  c.c.  of  con- 
tents (B2),  we  have,  as  a  result  of  our  subtraction,  the  total  organic 
acids  (see  addenda  to  analysis). 
This  plan  of  analysis  is,  as  I  have  stated,  a  modification  of  the 
method  published  by  Topfer.48    The  modifications  consist  in  : 
(1)  The  addition  of  the  Congo  red  test  for  free  acids  and  acid 
salts  to  the  alizarin  test  as  given  by  Topfer,  in  the  quantitative  esti- 
mation of  these  substances. 
(2)  The  substitution  of  the  phloroglucin-vanillin  test  for  HC1,  for 
the  di-methyl-amido-azo-benzol  test  of  Topfer  in  the  quantitative 
estimation  of  the  HQ. 
The  reasons  for  these  changes  are  given  in  the  description  of  the 
methods  (see  preceding  pages).  As  I  have  stated  in  the  description 
referred  to,  the  Topfer  tests  are  satisfactory  for  a  majority  of  cases 
examined,  but  not  for  many  cases,  especially  those  with  patho- 
logical conditions.  The  objections  to  the  tests  cited  are  based  upon 
the  researches  of  Hari,49  Strauss,50  Mohr,51  and  upon  my  own  expe- 
rience in  analyses  of  the  gastric  contents. 
The  pepsin  of  the  gastric  juice  is  produced  from  the  pepsinogen 
formed  in  the  glands  of  the  gastric  mucous  membrane  by  the  action 
of  free  hydrochloric  acid  upon  this  pepsinogen.52  Since  pepsin  may 
be  found  in  gastric  contents  containing  no  free  hydrochloric  acid,  it 
is  probable  that  the  secreted  acid  has  combined  with  the  pepsinogen 
before  the  affinities  of  the  proteid  foods  are  satisfied.53 
The  pepsin  acts  only  in  the  presence  of  free  hydrochloric  acid. 
The  evidence  of  the  presence  of  pepsin  in  the  contents  of  a  given 
case  is  assured  by  the  capacity  of  this  contents  to  digest  albu- 
min. 
If  free  hydrochloric  acid  be  present,  the  determination  of  the 
48  Topfer  :  Zeitschr.  /.  Physiol.  Chemie,  Bd.  XIX,  H.  1. 
49  Hari :  Archiv  f.  Verdauungskrankheiten,  Bd.  II,  H.  203. 
50  Strauss  :  Deutsches  Archiv </.  klin.  Med.,  Bd.  56,  H.  1. 
51  Mohr  :  Zeitschr.  f.  Physiolog.  Chemie,  Bd.  XIX,  H.  6,  s.  6,  H.  7. 
52  Langley  :  Journal  of  Physiology,  Vol.  VII,  p.  391,  and  Vol.  Ill,  p.  269. 
53  Hammerschlag  (Archiv  f.  Verdauungskrankheiten)  finds  considerable 
amounts  of  pepsin  in  cases  with  no  free  HC1. 
