A  tubercle  from  a  case  of  tuberculosis  of  the  liver.  A  multinucleated  giant-cell
occupies  the  centre.  Around  is  an  area  of  commencing  caseation  and  outside
this  a  zone  consisting  principally  of  fibroblasts,  and,  to  a  less  extent,  of  leuko-
cytes. The  leukocytes  are  most  numerous  on  the  side  where  caseation  is
most  advanced.  X  250.
thelioid  cells  we  find  a  layer  of  smaller  lymphoid  cells,  both
often    being    supported   by  a  fine   connective-tissue    reticu-


266     PATHOLOGY  OF  THE  BLOOD  AND  CIRCULATION.
him.  Such  an  arrangement  of  epithelioid  and  lymphoid
cells,  with  often  a  large  multi  nucleated  giant-cell  in  their
centre,  constitutes  the  typical  histological  tubercle  (see  Fig.
106).
The  structure  of  these  tubercles,  however,  varies  consider-
ably ;  in  some  instances  the  leukocytic  migration  is  so  great
as  almost  to  hide  the  epithelioid  cells.  If  properly  stained,  the
tubercle  bacillus  may  be  found  between  the  epithelioid  cells
first  formed ;  later  they  are  more  numerous,  many  being
within  the  cells,  especially-  within  the  giant-cells.
The  giant-cell  was  at  one  time  supposed  to  be  typical  of
tuberculosis,  but  it  is  now  known  to  be  frequently  found  in
other  chronic  inflammatory  processes,  and  in  some  tumor-
formations,  though  neither  so  abundant  nor  so  conspicuous.
They  often  have  as  many  as  fifteen  to  twenty  nuclei  arranged'
around  the  periphery  of  the  cell  or  at  either  of  its  poles.  By
some  observers  the  giant-cells  are  supposed  to  result  from
the  rapid  multiplication  of  the  nuclei  of  the  epithelioid  cells
without  division  of  the  cell-protoplasm  ;  according  to  Metsch-
nikoif  and  others,  they  result  from  the  running  together  of
the  phagocytic  leukocytes  and  epithelioid  cells,  combining,  as
it  were,  for  a  common  weal.
