on  either  side,  that  it  may  readily  be  placed  over  a  tooth.  To  this  is
attached  a  sac  of  finely-prepared  membrane  large  enough  to  hold  a
table-spoonful  of  the  mixture.  The  hollow  of  the  tube  is  occupied  by
a  steel  wire  spiral  spring.  Just  before  using  it,  a  sufficient  quantity
of  the  freezing  mixture  is  put  in  the  tube ;  the  end  of  the  latter  is
placed  over  the  tooth,  when  the  ice  and  salt  are  forced  up  gently
around  it  by  pressing  on  the  spring  at  the  other  extremity  of  the
instrument.  Two  tubes  are  employed,  one  straight  for  teeth  in  the
anterior  part  of  the  mouth,  the  other  bent  near  one  end  for  the  more
convenient  application  of  the  mixture  to  a  molar  tooth.
The  sudden  application  of  such  intense  cold  to  a  sensitive  tooth,  or
to  one  which  has  not  lost  its  vitality,  is  often  productive,  at  first,  of
severe  pain ;  on  this  account  many  object  to  the  use  of  it,  preferring
the  momentary  sufiering  consequent  upon  the  operation  of  extraction
than  that  occasioned  by  the  freezing  mixture.  But  this  effect  is  rarely
experienced  in  its  use  on  dead  teeth  or  the  roots  of  teeth  which  have
lost  their  vitality;  hence,  the  application  of  it  has  to  such  proved  more
satisfactory  than  to  living  teeth.
