The  practical  conclusions  of  Laennec,  Clark,  Bennett,  Pollock,
^md  other  scientific  observers  are,  that  if  the  further  growth  of
tubercle  can  be  arrested,  those  already  existing  may  diminish  in
size,  become  absorbed,  and  the  parts  cicatrize;  or  they  may  remain
dormant,  without  exciting  any  symptoms,  after  undergoing  a
process  called  cretification,  in  which  the  animal  portion  is  absorbed,
the  earthy  only  remaining.  Frequently,  however,  from  defective
hygienic  conditions,  or  other  cause,  tubercles  undergo  a'  succes-
sion of  changes;  they  first  become  soft  in  the  center,  that  part
being  the  oldest  and  most  removed  from  living  influences;  then,
like  foreign  bodies,  they  excite  inflammation,  suppuration,  and
ulceration  in  the  neighboring  tissue.  The  groups  often  continue
to  enlarge  till  several  groups  conmiunicate  and  form  a  vomica;
this  bursts,  and  when  the  lirngs  are  the  organs  involved,  its
contents  are  discharged  into  an  adjacent  bronchial  tube,  and  the
matter  is  conveyed  into  the  windpipe,  and  thence  to  the  mouth,  to
be  evacuated.  Unless  the  disease  be  arrested,  other  Abscesses
form  and  unite,  till  the  lung-substance  is  so  diminished  in  volmne,
and  its  continuity  so  completely  destroyed,  as  to  be  incompatible
mih  life,  and  the  patient  dies  of  exhaustion.  In  other  cases,  the
tubercular  matter,  with  the  inflammatory  products  it  excited,  are
removed  by  expectoration  or  absorption,  the  tissues  around  the
cavity  contract  and  obliterate  it,  and  so  the  disease  is  cured.
The  parts  most  commonly  affecte<l  by  tubercle  are — ^the  lungs,
the  brain  and  its  membranes,  the  intestines,  the  liver,  the  peri-
cardium, and  the  peritoneum.
