of  resisting  the  effects  of  cold.  It  has  been
stated  that  comma-bacilli  exposed  to  a  tempera-
ture of — 10°  for  an  hour,  and  bacilli  of  anthrax
after  exposure  to  a  temperature  of — no°C.,  still
retained  their  vitality.  Temperatures  over  50°  to
60°  C.  destroy  most  bacteria,  but  not  their  spores  ;
spores  of  anthrax  retain  their  vitality  after  im-
mersion in  boiling  water,  but  are  destroyed  by
prolonged  boiling.  Roughly  speaking,  all  patho-
genic bacteria  grow  best  at  the  temperature  of
the  blood,  and  non-pathogenic  bacteria  at  the
ordinary  temperature  of  the  room.
Effect  of  Movement. — Bacteria  probably  grow
best  when  left  undisturbed.  Violent  agitation  of
a  vessel  in  which  they  are  growing  certainly
retards  their  growth,  but  a  steady  movement  is
stated  not  to  affect  it  ;  at  any  rate  anthrax  bacilli
grow  with  enormous  rapidity  in  the  blood-vessels,  in
spite  of  the  circulation.
Effect  of  Compressed  Air. — Paul  Bert  maintained
that  a  pressure  of  twenty-three  to  twenty-four
atmospheres  stopped  all  development  of  putre-
factive bacteria.  Oxygen,  under  a  pressure  of  five
or  six  atmospheres,  is  stated  to  stop  their  growth.
Other  observers  have,  however,  obtained  different
•results.
Effect  of  Gases. — Hydrogen  and  carbonic  acid  are
stated  to  stop  the  movements  of  the  motile  bacteria.
Chloroform  is  believed  to  arrest  the  changes  brought
about  by  the  zymogenic  species.
GENERAL    MORPHOLOGY    AND    PHYSIOLOGY.        171

Electricity. — Cohn  and  Mendelsohn  found  that
a  constant  galvanic  current  produced  a  deleterious
effect  owing  to  electrolysis.  At  the  positive  pole
the  liquid  became  distinctly  acid,  and  at  the
negative  pole  distinctly  alkaline.  With  a  weak
current  there  appeared  to  be  no  effect,  two  power-
ful cells  at  the  very  least  being  necessary.
