The  anatomical  changes  in  fever,  due  to  the  increased  tem-
perature alone,  are  few.  It  is  difficult  to  separate  the  results
produced  by  the  high  temperature  from  those  produced  by  its
exciting  cause.  Cloudy  swelling  and  fatty  degeneration  of  the
heart,  liver,  and  kidneys,  are  probably  in  part  due  to  the  fever
itself,  though  in  part  undoubtedly  to  toxic  substances  circu-
lating in  the  blood.
THE  CIRCULATORY  APPARATUS.
Hyperaemia  is  an  increase  in  the  amount  of  blood  in  a  part :
and  is  either  actual,  due  to  an  increase  of  the  flow  to  the
part ;  or  passive,  due  to  an  obstruction  of  the  outflow.
Active  hyperaBmia :  Blushing  is  a  physiological  example.
Pathologically  it  is  hardly  met  except  associated  with  some  of
the  phenomena  characteristic  of  inflammation.  A  variety
due  to  vaso-motor  paralysis,  as  seen  in  experimental  section  of
the  cervical  sympathetic  in  animals,  is  occasionally  met  with
clinically,  as  after  gunshot-wound  of  the  same  nerve.
270     PATHOLOGY  OF  THE  BLOOD  AND   CIRCULATION.
Passive  hypersemia  is  produced  locally  by  thickening  of
venous  walls,  external  pressure  on  the  veins  of  a  part  by  a
tumor,  gravid  uterus,  etc.  Cardiac  weakness  produces  a  gene-
ral venous  congestion  finally,  if  severe  enough,  of  all  the  tis-
sues of  the  body.
The  consequences  of  venous  congestion  are  more  important
than  those  of  active  congestion — the  blood-serum  transudes  in
greater  quantities  than  can  be  removed  by  the  lymphatics,  and
the  tissues  become  cedematous  and  swollen.  In  the  internal
organs  there  may  result  pressure-atrophy  of  the  true  paren-
chyma-cells and  an  increase  of  the  connective-tissue  elements.
FIG.  108.
Section  of  white  thrombus  containing  few  leukocytes,  a,  granular  masses ;  &,  granu-
lar threads  of  fibrin  arranged  in  a  network  ;  c.  parallel  arranged  threads  of  fibrin.
X  200  (Zeigler).
