28  Modern  Surgical  Dressings.  {^£££8$^ 
because  any  bacteria  present  will  be  found  upon  their  outer  surface  ; 
but  when  bacteria  are  enclosed  in  a  rock-like  mass,  as  they  are  in 
dried  dust  particles,  where  we  find  them  surrounded  by  an  almost 
impenetrable  fortress,  in  dried  pus,  sweat,  in  dried  secretions  or 
flesh  tissue,  these  organisms  are  protected  by  a  varnish-like  coating. 
Bacteria,  within  the  fibre  of  cotton  or  wool,  are  enclosed  within  a 
cellulose  structure.  Therefore,  in  the  disinfection  of  cotton,  wool, 
silk,  sponge  and  catgut,  we  find  that  there  is  presented  a  varying 
problem  with  each  material.  Chemical  reaction  is  also  a  factor  in 
disinfection  that  has  been  long  overlooked.  In  the  disinfection  of 
dressings  the  nature  of  the  materials  and  their  behavior  toward  the 
disinfecting  agent  must  be  taken  into  account.  Thus  cotton  may 
be  disinfected  in  a  solution  of  soda,  but  wool  thus  treated  would  be 
destroyed. 
Wool  may  be  disinfected  in  an  acid  solution,  which,  in  turn, 
would  destroy  cotton.  Catgut  is  affected  by  most  chemicals;  it  is 
destroyed  by  moisture.  Sponge  tissue  is  affected  by  many  chem- 
icals ;  it  is  destroyed  by  moist  heat.  Oily  substances  are  impene- 
trable by  watery  solutions. 
The  sole  universal  disinfectant  is  fire.  It  destroys  the  infection 
and  the  infected  material.  It  is  applicable  to  the  disinfection  of 
asbestos  dressings,  which  have  recently  been  recommended  for  sur- 
gical purposes.  There  is  no  one  method  or  agent  which,  under  all 
circumstances,  will  meet  all  conditions.  Generally,  more  than  one 
agent  and  several  methods  of  procedure  must  be  used  together  or 
in  succession. 
The  writer  has  made  a  long  series  of  investigations,  having  in 
view  the  possibility  of  disinfecting  dressings  with  agents  that  would 
have  no  reaction  with  the  material  composing  the  dressing,  that 
could  be  readily  removed  from  the  dressing,  or,  when  allowed  to  re- 
main [within  the  dressing  material,  would  have  no  effect  upon 
wound  tissue.  In  these  experiments,  such  agents  as  electricity, 
gases,  vapors,  friction  and  pressure  were  employed. 
The  general  method  pursued  was  to  infect  fibres  with  a  nutrient 
fluid  containing  bacteria,  to  then  subject  the  infected  fibres  to  the 
action  of  the  disinfecting  agent.  The  results  may  be  briefly  sum- 
marized. 
Electricity  was  not  effective  upon  the  organisms,  except  when 
electrolysis  took  place,  as  was  the  case  when  water  or  a  solution 
