34  Analysis  of  the  Gastric  Contents.     { ^SyfmT' 
(4)  The  quantitative  estimation  of  the  total  secreted  hydrochloric 
acid,  that  is,  the  free  plus  the  combined  hydrochloric  acid. 
The  hydrochloric  acid  secreted  by  the  stomach  during  digestion 
is  disposed  of  in  four  ways.  One  portion  combines  with  the  inor- 
ganic bases  of  the  food  or  of  the  saliva. 
As  the  Ewald  meal  is  in  infusion  acid,  the  amount  of  acid  used  in 
this  way  in  cases  examined  by  this  method  is  practically  that  neces- 
sary to  neutralize  alkaline  salts  of  the  saliva. 
This  portion  of  the  hydrochloric  acid  is  not  adaptable  for  the 
digestion  of  the  food,  and  does  not  appear  in  the  quantitative  deter- 
minations of  acidity. 
A  second  portion  combines  with  the  proteid  or  albuminoid  sub- 
stances, either  normal  in  the  stomach,  as  mucin,  epithelial  cells, 
pepsinogen,  rennin  zymogen,  or  produced  there  in  pathological  con- 
ditions. 
A  third  portion  combines  with  the  organic  bases  of  the  food,  the 
proteid  elements — to  form  acid  proteids. 
A  fourth  portion,  which  appears  only  when  the  first  three  portions 
are  completed,  exists  as  free  acid. 
These  last  three  portions  make  up  the  total  acid  adaptable  for 
purposes  of  digestion.  They  all  appear  in  the  quantitative  deter- 
mination of  the  hydrochloric  acid — the  first  two  as  combined  acid, 
the  third  as  free  acid. 
The  purely  digestive  function  of  the  hydrochloric  acid  is,  then, 
{a)  to  completely  combine  with  the  proteid  food  elements ;  (b)  to 
combine  with  the  pepsinogen  and  rennin  zymogen,  to  liberate  the 
ferments ;  (c)  to  serve  as  free  acid,  as  a  menstruum  for  the  action  of 
the  pepsin  upon  the  acid  proteid  combinations. 
The  object  of  our  analysis  in  a  given  case  is  to  determine  if  a 
sufficient  amount  of  hydrochloric  acid  is  secreted  to  perform  this 
function. 
From  what  has  been  said  concerning  the  action  of  the  acid,  it  is 
clear  that  this  object  is  in  some  measure  attained  by  the  determina- 
tion of  the  presence  in  the  contents  of  free  hydrochloric  acid.  Free 
acid  present,  we  have  the  proteid  affinities  saturated,  the  ferments 
liberated  and  the  conditions  for  peptic  digestion  present. 
Even  with  free  acid  present,  however,  a  more  definite  knowledge 
of  the  comparative  vigor  of  the  digestive  function  in  a  given  case 
can  be  obtained  by  the  determination  of  the  total  hydrochloric  acid. 
