The  most  valuable
advantage  is  that
indicated  by  its
great  output  for
deep  therapeutic
work,  and  also  for
instantaneous
radiography.  There
is  a  note  of  warn-
ing which  it  is

well  to  put  forward,  and  that  is  that  this  tube
gives  little  or  no  visible  sign  of  fluorescence,  so
that  extra  precautions  must  be  taken  ;  otherwise,
owing  to  its  much  greater  output,  and  the  fact
that  the  tube  will  continue  to  give  a  steady  flow
of  radiation,  a  serious  burn  can  be  produced  if
careful  measurement  of  the  dose  is  not  employed,

10


FIG.  22.— Complete  Coolidge  X-ray
equipment  in  position.     (B.T.H.)


146        GENERAL  PRACTICE  AND  X-RAYS

whereas  the  ordinary  form  of  tube  cannot  be  con-
tinuously run  with  a  heavy  current.  A  tube
designed  by  Lillienfeld  is  also  constructed  to
work  with  a  "  hot "  cathode.  It  is  somewhat
more  complicated  than  the  Coolidge  tube.
FIG.  23. — Diagram  of  connections  for  Coolidge  tube.
S,  Spark-gap.
M,  Milliammeter.
B,  Storage  battery.
K,  Rheostat  for  controlling  current
in  the  filament  circuit.
A,  Ammeter  for  measuring  current
in  filament  circuit.
