The  quality  of  a  sound  is  that  property  which  enables  us  to  recognize
it  whenever  heard  without  seeing  the  mechanism  by  which  it  is  prod^ced,
as  the  sound  of  a  bell,  a  drum,  and  so  on;  the  volume  or  intensity  of  a
sound  relates  to  the  energy  and  the  mass  of  the  material  by  which  it  is
produced,  as,  for  example,  in  great  and  little  bells,  the  sound  of  which  has
the  same  quality  and  may  have  the  same  pitch  while  differing  greatly  in
intensity  or  volume;  the  pitch  depends  upon  the  rapidity  of  the  vibrations
by  which  sound  is  produced,  as  in  the  long  strings  of  the  piano  which  pro-
duce low  notes,  and  the  short  strings  which  send  forth  the  high  notes.
The  Lung  Reflex  (Abrams).  —  It  has  been  observed  that  local
irritation  of  the  skin  of  the  chest  as  by  cold  or  the  application  of  mustard
has  been  followed  by  the  evidences  of  a  temporary  circumscribed  emphy-
sema of  the  underlying  lung.  These  signs  of  dilatation  of  the  air-vesicles
have  in  some  instances  been  confirmed  by  X-ray  examination.  Cabot
has  referred  to  this  observation  in  explanation  of  the  fact,  well  known  to
teachers  of  physical  diagnosis,  that  the  repeated  demonstration  of  an  area
of  moderate  dulness,  as,  for  example,  in  incipient  tuberculosis,  is  followed
by  a  modification  of  the  percussion  sign,  which  graduall)'  becomes  more
resonant.  The  repeated  percussion  apparently  acts  as  a  local  irritant.
If  the  consolidation  is  dense  and  extensive  this  change  cannot  occur.
