NITRATE  OF  AMMONIA  AND  NITROUS  OXIDE. 
411 
patient  to  inhale  directly  from  the  gasometer.  Others  prefer 
taking  the  gas  from  the  gasometer  as  it  is  wanted,  in  an  India- 
rubber  bag,  from  which  it  is  administered.  It  is  only  necessary, 
when  the  bag  is  to  be  filled,  to  connect  it  by  tubing  with  the 
supply-cock  of  the  gasometer,  and  by  a.  little  downward  pressure 
on  the  receiver  the  gas  will  be  forced  into  the  bag.  The  capacity 
of  the  bag  should  not  be  less  than  eight  gallons,  although  when 
breathed  in  and  out,  as  some  operators  administer  it,  six  gallons 
or  less  will  generally  produce  anaesthesia.  This  effect  usually 
occurs  in  from  thirty  seconds  to  a  minute  and  a  half ;  insensi- 
bility to  pain  is  oftentimes  reached  before  the  patient  is  entirely 
unconscious.  Anaesthesia  is  generally,  although  not  invariably, 
manifested  by  snoring,  but  it  is  not  always  necessary  to  carry  the 
effect  to  this  point ;  and,  notwithstanding  the  assurances  to  the 
contrary,  there  are  many  who  do  not  believe  that  profound  an- 
aesthesia, produced  by  any  agent,  is  entirely  free  from  danger. 
At  all  events,  it  is  the  dictate  of  prudence  to  proceed  no  further 
than  is  absolutely  indispensable.  It  is  customary  to  hold  the 
nose  of  the  patient  so  that  no  atmospheric  air  is  mixed  with  the 
gas  inhaled  ;  but  this  practice  is  energetically  opposed  by  some, 
who  assert  that  an  admixture  of  air  is  positively  necessary  to  the 
safety  of  the  patient. 
It  is  administered  by  some  practitioners  to  every  patient  who 
presents,  without  regard  to  the  state  of  the  health  ;  but  there  is 
reason  to  believe  'that  caution  should  be  observed  in  this  direc- 
tion, and  that  it  should  not  be  given  to  those  having  heart  disease, 
who  are  predisposed  to  apoplexy,  or  whose  lungs  are  seriously 
affected,  nor,  as  a  rule,  in  any  case  where  there  is  serious  dis- 
turbance of  vital  functions.  The  unconscious  state  usually  con- 
tinues from  a  half  to  one  minute,  and  in  two  to  three  minutes 
almost  all  return  to  a  perfectly  normal  condition.  If  the  opera- 
tion is  protracted,  more  gas  can  be  given  when  sensibility  to  pain 
returns. 
Dr.  Geo.  J.  Ziegler,  who  has  carefully  investigated  the  pro- 
perties of  this  agent,  claims  that  "  nitrous  oxide  is  very  efficient 
as  a  restorative.  It  may  be  administered  either  in  its  gaseous 
state  by  the  lungs,  or  in  conjunction  with  liquids  by  the  aliment- 
ary canal.    It  should  be  given  gradually  in  moderate  quantities, 
