434         DISINFECTANTS  IN  ARRESTING  CATTLE  PLAGUE. 
McDougall's  disinfecting  powder  ;  its  good  effect  therefore  does 
not  cease  as  soon  as  the  atmosphere  is  free  from  its  odor. 
The  gaseous  acid  has  a  great  affinity  for  water ;  the  natural 
moisture  always  present  in  clothing,  or  on  the  wood-work  and 
other  parts  of  cow-sheds  most  likely  to  retain  infection,  is  able  to 
absorb  the  gas  in  quantity  sufficient  to  form  a  solution  in  contact 
with  which  virus  cells  cannot  exist.  When  absorbed  in  this  man- 
ner it  is  only  very  slowly  evolved, — a  fact  which  has  been  noticed 
by  all  who  have  been  in  sheds  whilst  undergoing  this  mode  of 
purification, — the  fumes  of  the  burning  sulphur  being  said  to 
"  hang  about"  the  clothes  for  a  considerable  time.  Articles  of 
clothing,  boots,  tools,  sacks,  baskets,  pails,  ropes,  and  any  other 
portable  article  which  may  require  disinfection,  are  conveniently 
purified  by  allowing  them  to  remain  in  a  close  shed  whilst  it  is 
undergoing  sulphur  fumigation. 
Sulphurous  acid,  in  addition  to  its  antiseptic  qualities,  is  a 
deodorizer  of  considerable  energy.  It  destroys  the  powerful 
odor  of  most  of  the  offensive  gases  named  in  paragraph  12.  It 
attacks  and  oxidizes  sulphuretted  hydrogen,  entirely  destroying 
it ;  it  neutralizes  the  strong  smell  of  ammonia  and  other  alkaline 
bases,  converting  them  into  sulphites,  but  without  destroying 
their  manurial  value  or  losing  its  antiseptic  properties.  In  this 
respect  it  differs  in  an  important  manner  from  chlorine. 
The  use  of  sulphurous  acid  is  open  to  one  or  two  objections. 
When  absorbed  on  clothing  or  damp  wood-work,  it  gradually 
oxidizes  into  sulphuric  acid.  In  cow-sheds  this  is  not  of  much 
consequence,  as  there  is  always  sufficient  ammonia  present  to 
neutralize  it ;  but  if  repeatedly  formed  on  clothing,  it  will  bleach 
the  articles,  and  ultimately  make  them  rotten.  When  neutralized 
with  lime  or  ammonia,  or  other  bases,  the  antiseptic  value  of  the 
sulphurous  acid  is  not  impaired,  but  it  is  tied  down  to  one  spot, 
and  prevented  from  acting  in  the  atmosphere.  When  the 
sulphites  thus  formed  are  allowed  to  remain  in  contact  with  wet 
organic  matter,  they  gradually  decompose  with  evolution  of 
sulphuretted  hydrogen ;  but  this  decomposition  is  stopped  at 
once  by  an  additional  fumigation  with  sulphur,  and  if  the  sheds 
are  cleaned  out  every  day  it  will  never  occur.  Sulphites  have 
been  used  with  success  by  Prof.  Polli  and  Dr.  De  Ricci,  both  as 
