26  Analysis  of  the  Gastric  Contents.  {ArjkSaryfih898.m' 
digestion  in  health  and  disease.  This  knowledge  is,  stated  briefly, 
as  follows  : 
The  digestion  of  food  in  the  stomach  occurs  through  the  agency 
of  a  mineral  acid  (hydrochloric  acid),  a  proteolytic  ferment  (pepsin) 
and  a  coagulating  ferment  (rennin),  all  produced  from  the  glands  of 
the  mucous  membrane  of  the  stomach.  Under  the  combined  action 
of  these  physiological  agents  the  proteid  elements  of  the  ingested 
food  are  digested. 
The  secretion  of  the  hydrochloric  acid  begins  immediately  upon 
the  ingestion  of  the  food.  The  secreted  acid  at  once  combines  with 
the  native  proteids  of  the  food,  forming  acid  proteids.  It  also  acts 
upon  the  pepsinogen  in  the  gastric  glands  forming  pepsin.2  The 
secretion  of  the  acid  continues  until  the  affinities  of  the  native  pro- 
teids for  acid  being  satisfied,  a  certain  amount  of  superfluous  (free) 
hydrochloric  acid  obtains  in  the  stomach. 
Coincident  with  the  appearance  of  this  free  hydrochloric  acid,  the 
activity  of  the  pepsin  ferment  begins.3  Under  the  influence  of  this 
pepsin  in  free  HC1,  the  acid  proteid  products  are  converted  with 
increased  rapidity  to  albumoses  and  peptones.  The  rennin  ferment 
is  produced  from  the  beginning  of  digestion,  in  part  existing  pre- 
formed  in  the  cell  of  the  mucous  membrane,  in  part  being  formed  by 
the  action  of  the  secreted  acid  upon  the  rennet  zymogen.  Under 
its  influence  the  casein  of  food  is  digested  to  a  coagulated  and  a 
soluble  proteid.4 
The  products  of  digestion  are  in  part  absorbed,  in  pari  expelled 
in  small  quantities  during  the  process  of  digestion.  The  greater  part 
of  the  contents  is,  however,  expelled  en  masse  into  the  duodenum  at 
the  completion  of  digestion  (Richet  and  Kiihne).  Whatever  pro- 
ducts are  absorbed  are  replaced  by  water  secreted  by  the  stomach. 
The  mixed  contents  of  the  stomach  will  contain  in  the  earlier 
stage  of  digestion  : 
(1)  The  elements  of  the  ingested  food,  proteids,  albuminoids,  car- 
bohydrates, fats,  mineral  and  organic  salts  and  extractives. 
(2)  The  acid  proteids  and  acid  salts,  the  products  of  the  combina- 
tion of  the  secreted  hydrochloric  acid  with  the  proteids  and  mineral 
salts  of  the  food. 
2  Langley  :  Journal  of  Physiology,  Vol.  Ill  and  Vol.  VII. 
3 Boas:  Diagnostikd.  Magenkrankheiten,  Leipzig,  1890,  s.  118. 
4  Hatnmarsten  :  Maly's  Jahresbericht,  Vol.  II,  p.  118  ;  Vol.  IV,  p.  135  ;  Vol. 
VII,  p.  158. 
