The  vomit  itself  usually  consists  of  an  opalescent  fluid,
often  stained  yellow  or  green  with  bile,  and  possessing  a  sour
taste  and  smell  and  an  acid  reaction.  When  ejected  during
the  period  of  gastric  digestion  the  material  rapidly  separates
in  the  test-glass  into  two  layers,  the  lower  of  which  presents
the  opaque  appearance  and  dirty  grey  colour  significant  of  un-
digested particles  of  food,  while  the  upper  one  is  comparatively
clear,  often  coloured  with  bile,  and  covered  by  a  thick  layer
of  froth.  The  material  is  acid  to  litmus-paper  and  always  con-
tains free  hydrochloric  acid  and  the  special  gastric  ferments.
Its  total  acidity  varies  from  40  to  70.  It  is  consequently
capable  of  digesting  threads  of  fibrin  when  kept  in  a  warm
chamber,  and  of  curdling  milk  after  neutralisation  with  bi-
carbonate of  sodium.  The  sediment  is  found  to  consist  of
starch,  vegetable  fibre,  shreds  of  meat,  epithelial  cells,  and
food  debris.
In  rare  instances  there  is  great  intolerance  of  fat,  and  in
such  the  vomit  may  be  like  liquid  butter  or  after  standing
present  a  soft  crust  of  fat.  In  such  cases  chronic  duodenitis
with  pancreatitis  usually  exists  and  is  very  often  of  syphilitic
origin.
From  time  to  time  attacks  of  acute  hypersecretion  are  apt  to
supervene,  as  the  result  of  which  gastric  intolerance  becomes
established,  and  the  patient  suffers  from  incessant  retching  and
vomiting.  In  these  circumstances  only  an  ounce  or  two  of
a  green  mucoid  fluid  may  be  vomited  on  each  occasion,  and
the  proportion  of  free  hydrochloric  acid  contained  in  it  falls
considerably  below  the  former  standard.
