200 
Formaldehyde. 
Am.  Jonr.  Pharm. 
April,  1898. 
lamp  is  lighted  and  this  evaporating  chamber  is  brought  to  a  red 
heat,  a  valve  controlling  the  opening  of  the  tube  from  the  receiver 
to  the  evaporating  chamber  is  opened  and  the  formaldehyde  solu- 
tion is  allowed  to  trickle  down  in  a  fine  stream  into  the  heated 
chamber.  It  is  then  instantly  vaporized,  the  intense  heat  breaks 
up  the  polymerised  products,  and  the  pure  gas  is  delivered  through 
the  delivery-tube  and  is  conducted  into  the  apartment. 
Dr.  W.  H.  Park  and  Dr.  Arthur  R.  Guerard  made  a  long  series 
of  bacteriological  tests  to  determine  the  apparatus  best  adapted  for 
the  use  of  the  New  York  City  Health  Department. 
These  tests  were  very  thorough  and  comprehensive  ;  they  proved 
that  formaldehyde  could  be  depended  upon  to  produce  thorough 
.  surface  disinfection ;  that  its  use  did  not  affect  colors  or  metals  in 
any  way,  and  that  the  cost  of  disinfection  was  not  greater  than 
when  sulphur  was  used. 
In  their  published  reports,  many  investigators  have  stated  that 
they  are  unable  to  get  satisfactory  sterilization  with  formaldehyde. 
I  have  investigated  many  of  these  cases  and  in  nearly  every  instance 
have  found  that  the  failure  was  not  due  to  the  lack  of  germicidal 
power  in  the  gas,  but  because  too  much  had  been  expected  of  it,  and 
because  the  test  organisms  had  not  been  freely  exposed  ;  one  might 
think  that  a  culture  placed  in  an  open  test  tube  was  freely  exposed, 
but  this  has  proved  to  be  an  extremely  severe  condition,  as  the  gas 
is  required  to  replace  a  closed  pocket  or  cushion  of  air.  The  same 
objection  can  be  held  against  the  practice  of  exposing  cultures  in 
boxes  with  perforated  sides  or  covers.  Other  experimenters  have 
wrapped  the  cultures  in  filter  paper,  a  substance  which  is  practically 
impenetrable  by  the  gas. 
The  method  which  has  been  generally  adopted  as  being  the  most 
satisfactory  and  as  giving  the  most  uniform  results  is  as  follows: 
Loosely  twisted  threads  of  cotton  are  steeped  in  virulent  cultures 
of  pathogenic,  non-spore-bearing  bacteria.  These  threads  are  dried 
and  half  of  each  thread  is  cut  off  and  reserved  as  a  check  on  the 
result.  The  other  half  is  placed  on  a  strip  of  sterilized  paper  and 
freely  exposed  for  six  hours  to  the  action  of  the  gas  generated  from 
six  ounces  of  formaldehyde  solution.  The  threads  are  then  placed 
in  tubes  containing  the  medium  best  adapted  for  the  growth  of  the 
organisms  employed  and  kept  in  an  incubator  for  from  46  to  70 
hours.    If,  at  the  end  of  that  time,  a  growth  of  the  specified  bacteria 
