-  a


6  —


Serous  leptomeningitis.  a,  cedematous  fibrous  tissue  of  the  pia  mater,  the  fibrous
elements  of  the  tissue  being  separated  by  the  serous  exudate ;  6,  group  of  leuko-
cytes, probably  held  together  in  part  by  fibrin ;  c,  granular  fibrin  and  detritus  :  6
and  c  and  other  similar  masses,  lie  in  the  serum,  which  occupies  the  whole
field  between  the  visible  elements  (Dunham).
regions  of  the  body,  most  commonly  the  lungs.  The  miliary
tubercles  are  most  numerous  in  the  pia  at  the  base  of  the
brain.  The  meninges  are  congested,  and  may  be  the  seat  of
exudations  similar  to  those  occurring  in  simple  meningitis.
The  ventricles  of  the  brain  are  distended  with  a  serous  exu-
date and  their  walls  studded  with  miliary  tubercles.  The


424  DISEASES  OF  THE  NERVOUS  SYSTEM.
cortex  of  the  brain  is  congested  and  the  convolutions  flattened
by  pressure  from  within.
At  times  large  caseous  nodules  are  found  in  the  pia  mater
and  brain-tissue.
Syphilitic  inflammation  of  the  meninges  is  generally  circum-
scribed. The  gummata  which  form  involve  the  pia  and
the  cerebral  cortex,  or  they  may  extend  outward  and  involve
the  dura.
Tumors :  Endothelioma  is  probably  the  tumor  most  fre-
quently met  in  the  meninges.  Lipomata,  fibromata,  and
myxomata  are  of  rare  occurrence.
THE  BRAIN.
THROMBOSIS  AND  EMBOLISM.
The  results  of  thrombosis  and  embolism  in  the  brain  may
be  most  serious,  producing  death,  or  more  or  less  extensive
paralyses.
Emboli  are  brought  most  frequently  from  fibrinous  vegeta-
tion on  the  cardiac  valves,  or  from  cardiac  or  aneurysmal
thrombi.  They  generally  lodge  in  the  left  middle  cerebral
artery.
