DISINFECTANTS  IN  ARRESTING  CATTLE  PLAGUE.  433 
herds  of  Italy  yearly  purified  their  flocks  and  herds  with  burn- 
ing sulphur,  and  passages  in  other  writers  show  that  they 
averted  disease  from  them  by  this  means. 
Professor  Graham,  Master  of  the  Mint,  says,  that  of  gaseous 
disinfectants  "  sulphurous  acid  gas  (obtained  by  burning  sulphur) 
is  preferable,  on  theoretical  grounds,  to  chlorine.  No  agent 
checks  so  effectually  the  first  development  of  animal  and  vege- 
table life.  All  animal  odors  and  emanations  are  immediately 
and  most  effectually  destroyed  by  it." 
The  value  of  sulphurous  acid  in  arresting  the  progress  of  the 
cattle  plague,  has  been  proved  beyond  a  doubt  by  the  experi- 
ments of  Dr.  Dewar,  and  my  own  results  entirely  confirm  his. 
When,  however,  used  by  himself,  it  can  be  employed  only  very 
sparingly  in  sheds,  when  cattle  are  in  them  ;  it  is  very  stifling, 
and  its  powerful  deoxidizing  action  would  retard  the  conversion 
of  the  peroxide  of  iron  into  protoxide  by  the  act  of  respiration — 
a  result  equivalent  to  that  produced  by  breathing  an  atmosphere 
containing  less  than  its  normal  amount  of  oxygen,  which  has 
been  shown  by  Dr.  Angus  Smith*  to  be  incompatible  with 
health.  For  this  reason  I  prefer  to  use  it  only  as  an  additional 
precaution,  relying  principally  upon  other  agents.  Sulphurous 
acid  acts  in  many  cases  through  its  affinity  for  oxygen,  but  it 
possesses  also  great  antiseptic  powers  of  its  own,  so  that  a  slight 
exposure  to  it  is  sufficient  to  destroy  the  vitality  of  germs.  The 
following  experiment  proves  this  : — 
A  mixture  of  sugar  syrup  and  yeast  was  kept  in  a  warm  room 
until  it  became  in  a  state  of  active  fermentation.  An  aqueous 
solution  of  sulphurous  acid  was  added,  when  the  fermentation 
instantly  ceased.  When  examined  under  the  microscope  after 
treatment  with  sulphurous  acid,  no  apparent  change  was  ob- 
served in  the  appearance  of  the  yeast  cells. 
32.  When  sulphurous  acid  is  produced  in  a  white-washed 
shed,  it  unites  with  the  lime  on  the  walls,  forming  non-deliques- 
cent sulphite  of  lime,  one  of  the   valuable   ingredients  in 
*  "  Report  on  the  Air  of  Mines,"  by  R.  Angus  Smith,  Ph.  D.,  F.R.S., 
being  part  of  the  Appendix  to  the  Report  of  the  Royal  Mines  Commis- 
sion, London,  1864. 
28 
