504 
The  Action  etc.  of  Disinfectants, 
/Am.  Jouk.  Phaem. 
\    Nov.  1, 1873. 
there  is  absolutely  no  reason  for  believing  that,  by  the  employment 
either  of  the  one  or  of  the  other,  we  are  so  much  as  contributing 
towards  the  destruction  of  infection.  There  is  a  difference  not  only 
in  degree,  but  even  in  kind,  between  the  action  of  the  same  chemical 
when  concentrated  and  when  dilute.  Concentrated  sulphuric  acid  will 
convert  cane-sugar  into  a  lump  of  charcoal,  but  dilute  sulphuric  acid 
transforms  it  into  dextrin  and  glucose,  and,  curiously  enough,  fits  it 
for  undergoing  septic  changes.  So,  again,  very  dilute  bleaching  pow- 
der has  actually  been  found  to  favor  the  development  of  certain  low 
forms  of  life ;  and  Pettenkofer,  as  is  well  known,  has  found  that 
germs  whose  development  had  been  arrested  by  carbolic  acid,  start 
into  life  when  the  carbolic  acid  is  still  further  diluted. 
In  the  practical  employment  of  disinfectants,  the  fact  that  dilution 
frustrates  the  action  of  a  disinfectant  has  been  very  generally  lost 
sight  of.  Attempts  have  often  been  made  to  disinfect  the  atmosphere. 
It  is  even  said  that,  during  the  panic  occasioned  by  the  cattle-plague, 
the  commissioners  endeavored  to  disinfect  the  general  atmosphere  of 
the  agricultural  districts  by  turning  cattle  adrift  with  towels  soaked 
in  carbolic  acid  attached  to  their  horns.  I  need  not  insist  on  the 
futility  of  such  a  proceeding ;  or,  indeed,  on  the  necessary  futility  of 
any  effort  to  eliminate  anything  by  chemical  means  from  the  general 
atmosphere  covering  our-  fields  or  occupying  our  streets.  But  it  will 
probably  not  be  quite  needless  to  insist  upon  the  impracticability  of 
attacking  the  very  limited  atmosphere  of  a  dwelling-house  by  chemi- 
cal means.  Certain  very  simple  considerations  will,  however,  suflice 
to  throw  the  utmost  doubt  on  the  utility  of  endeavoring  to  purify  air 
which  has  suffered  contamination. 
In  a  well-known  official  memorandum,  drawn  up,  I  believe,  by  Pro- 
fessor Rolleston,  of  Oxford,  directions  are  given  for  the  disinfection 
of  a  room  with  sulphurous  acid.  So  much  sulphur  (the  quantity  pro- 
portionate to  the  size  of  the  room)  is  to  be  burnt,  and  doors  and  win- 
dows are  to  be  shut ;  and  the  memorandum  winds  up  with  the  state- 
ment that,  if  a  man  be  able  to  abide  in  the  room  for  one  instant  whilst 
the  disinfection  is  being  carried  on,  then  the  disinfection  is  not  to  be 
depended  upon.  In  other  words,  it  is  admitted  that,  not  until  you 
have  put  so  much  sulphurous  acid  into  the  air  as  to  make  it  totally 
unfit  to  breathe,  have  you  disinfected  that  air.  The  same  certainly 
holds  generally  in  regard  to  other  agents ;  and,  in  short,  we  cannot 
hope  to  purify  the  air  of  a  room  by  any  chemical  means  without  spoil- 
