DISINFECTANTS  IN  ARRESTING  CATTLE  PLAGUE.  429 
action  of  a  powerfully  oxidizing  disinfectant,  like  chlorine  or 
ozone,  upon  noxious  vapors  and  septic  germs.  In  presence  of  an 
excess  of  either  of  these  agents,  all  organic  impurity  is  at  once 
burnt  out,  and  reduced  to  its  simplest  combinations;  and  could  we 
always  rely  upon  the  presence  of  a  sufficient  amount  of  either  of 
these  bodies,  no  other  purifier  would  be  needed.  But  in  practi- 
cal work  on  a  farm  these  disinfectants  are  always  very  inade- 
quate, except  perhaps  for  half  an  hour  or  so  during  the  day ;  at 
other  times,  the  oxidizing  agent  has  presented  to  it  far  more 
noxious  material  than  it  can  by  possibility  conquer,  and  being 
governed  in  its  combinations  by  definite  laws  of  chemical  affinity, 
the  sulphuretted  and  carburetted  hydrogen,  the  nitrogen-  and 
phosphorus-bases,  &c,  would  all  have  to  be  burnt  up  before  the 
oxidizing  agent  could  touch  the  germs  of  infection;  whilst  the 
continued  renewal  of  the  gases  of  putrefaction  would  be  perpetu- 
ally shielding  the  infectious  matter  from  destruction. 
It  is  here  that  the  great  objection  lies  to  disinfectants  which 
act  by  oxidation.  If  we  arrange  in  a  series  (as  set'  forth  in  part 
12)  the  possible  substances  which  may  be  met  with  in  an  infected 
shed,  and  gradually  mix  with  them  chlorine  or  ozonized  air,  we 
find  that  those  vapors  having  strong  and  foetid  odors,  and  which 
stand  at  the  commencement  of  the  list,  are  the  first  to  go  ;  whilst 
the  actual  virus  of  the  disease — the  organized  particles  which 
have  no  odor  whatever — are  the  last  to  be  attacked.  But  in 
using  disinfectants  of  this  class,  the  only  test  of  efficiency  which 
a  workman  would  employ  is  the  sense  of  smell,  and  I  have  on 
several  occasions  known  it  happen  that  a  deodorized  shed,  to  all 
outward  appearances  disinfected,  was  still  in  reality  saturated 
with  infection.  It  so  happens  that  the  stinking  gases  of  decom- 
position are  of  little  or  no  danger  in  the  atmosphere,  whilst  the 
deadly  virus-cells  of  infectious  diseases  are  inappreciable  to  the 
sense  of  smell.  Mere  deodorization  is  therefore  no  protection 
whatever. 
The  following  experiment  tends  to  illustrate,  if  not  to  prove 
this  : — Cheese  mites  were  put  into  water  mixed  with  strongly 
smelling  cheese  and  sulphuretted  hydrogen.  Aqueous  solution 
of  chlorine  was  gradually  dropped  into  the  mixture  from  a 
burette.    The  smell  of  sulphuretted  hydrogen  was  the  first  to  go, 
