Hoch  and  Wolf hiigel  +  conclude  that  "  dry  heat,  even  continued  for
two  hours  at  150°  C,  did  not  always  assure  disinfection,  although
nothing  resisted,  even  for  a  few  minutes,  boiling  water  or  steam  at
100°  C."  Gaffky  and  Loffler§  summarise  their  experiments  as
follows  : —

*  Mittheilungen  aus  dew.  K.  Ge^undheitsamte,  vol.  i.,  p.  188.
+  See  also  Brit.  Med.  Journ.,  September  6,  1873.
J  Mitt.  a.  d.  Kais.  Gesundh.,  1881,  p.  301.  §  Ibid.,  p.  322.
DISINFECTI05   BY  HEAT.  33

1.  Non-spore-bearing  bacteria  cannot  endure  for  one  and  a-half
houi-s  an  exposure  to  hot  air  at  100°  C.
2.  The  spores  of  mould  are  not  killed  by  one  and  a-half  hours
exposure  to  hot  air  at  110°  to  115°  C.
3.  The  spores  of  bacilli  are  only  killed  by  three  hours  exposure  to
hot  air  at  140°  C.
Bonhoff  and  Foster  *  state  that  Bacillus  tuhercvlosis  at  60°  C.  dies
in  one  hour,  at  90°  C.  in  five  minutes,  and  at  95°  C.  in  one  minute.
The  experiments  of  Dr.  Klein  and  Dr.  Parsons,  as  detailed  in  the
Annual  Report  to  the  Local  Government  Board  for  1884,  confirm  very
largely  those  of  Koch,  and  they  also  deal  with  the  question  of  practical
disinfection  in  a  manner  that  renders  this  work  of  very  great  value.
The  great  advantages  of  steam  over  hot  air  were  demonstrated  very
clearly,  and,  owing  to  the  number  and  diversity  of  their  experiments,
they  were  able  to  show  that,  in  some  cases  at  all  events,  the  action  of
steam  in  a  suitable  apparatus  was  not  in  itself  injurious  to  the  articles
treated.
The  work  of  Pasteur,  Tyndall,  Lister,  Koch,  Parsons,  and  others
has,  therefore,  determined  the  fundamental  conditions  for  successful
disinfection  by  heat.
