HftiHtr's  ihiIhi'  is  the  amoimt  of  fatty  acid  insoluble  in  water,  which  can  tie
***'tained  by  the  saponification  of  too  gnis,  of  (at.  One  saponifies  a  weighed
"•WtiMjiit  of  fat,  evaporates  the  alcohol,  and  treat*  the  watery  ioliilion  of  the  rcsi-
^"e  with  hydrochloric  acid.  The  free  fatty  acid  is  treated  with  Ixiiling  water,
_*'''>«d,  and  weighed.
The  Reifhrri-ftitiul  value,  ihu  is,  llie  number  of  cubic  centlmoires  of  tenih-
'*^»"ni3l  potassium  hydrate  necexury  to  neuttalir.e  the  volatile  fatty  acid*  obtained
^y    the  sapoiiifiealion  of  5  sms.  of   fat.     One  saponifies  u  weighed  amount  of   fat,
^5'*'la'*'l   *'!*•   .^ulphuric   acid,   diitils   the    volatile   acid,   and   deietniines    in   the
Stillalc  the  amount  by  titration  with  leiilh-nonnal   KOH    (Thierfclder).
I


Mucus. — ^The  stools  always  contaiti  a  certain  amoiiiit  of  mucus
(Boas).  This  is  seltloni  seen  cveii  microscopically,  ami  musl  Iw
^*sie<l  for  chemically ;  atiy  amount  of  visilile  mticiis  is  somewhat  ah-
nomial.  The  mitciis  present  is  pure  mucin,  hence  cloittlcd  by  .icetic
*cid.  If  rnhlK-'i  up  wiili  water,  an  equal  ammint  of  lime  water  added.
left  to  stand  fi>r  several  hours  and  then  acetic  acid  he  adtled.  a  cloud
will  indicate  mnctis.
Muctts  is  incTcascil  ])liysiulopcalIy  as  the  result  of  hypersecretion.
This  forms  a  glassy  or  clundy  coating  over  hard  fecal  masses,  ami
evidently  serves  to  protect  the  inncntis  memhrnne.  It  is  poor  in  c«lls.
It  may  also  l)c  present  nftt-r  an  active  purRf.
