Exciting  Calse. — Pfeiffer — 1S92 — isolated  from  the  nasal  and  bron-
chial secretions  of  patients  suffering  from  influenza  a  bacillus  now  recognized
as  the  cause  of  the  disease.  It  occurs  in  great  numbers  in  the  nasal  secre-
tions and  is  frequently  seen  in  the  sputum  in  almost  pure  culture.  It
persists  in  the  secretions  for  some  time  after  the  symptoms  have  subsided.
The  disease  is  readily  transmissible  by  direct  contact  and  fomites;
also  to  short  distances  by  the  atmosphere.  Influenza  bacilli  are  destroyed
by  drjing,  and  rapidly  perish  in  water.  They  probably  enter  the  body  by
means  of  the  inspired  air.  Pfeiffer,  from  a  study  of  the  biological  char-
acters of  the  influenza  bacillus,  concludes  that  its  development  outside
the  human  body — that  is  to  say,  in  the  ground  or  in  water — is  imposfflble;
that  its  dissemination  when  dry  can  take  place  only  to  a  limited  extent,
and  that  the  contagium  is,  as  a  rule,  transferred  by  the  recent  moist  secre-
tion from  the  nasal  and  bronchial  mucous  surfaces  of  influenza  patient?.
Symptoms. — Influenza  presents  the  greatest  variations  as  regard*
intensity,  from  a  trifhng  indisposition  to  an  illness  of  the  gravest  kind.
In  every  epidemic  the  majority  of  the  sufferers  manifest  the  disease  in  a
mild  form,  very  many  in  a  rudimentary  form.     The  symptom-complex


INFLUENZA.
is  extremely  variable  and  greatly  modified  by  complications  and  sequels.
The  period  of  incubation  varies  from  a  few  hours  to  three  days.  Prodromal
symptoms  are  rare.  The  onset  is  abrupt,  marked  by  chilliness  or  a  chill
which  may  be  repeated.  There  is  fever,  headache  (usually  intense),  with
pain  back  of  the  eyeballs,  severe  pain  in  the  back,  limbs,  and  joints,  and
a  general  feeling  of  muscular  soreness  with  tenderness  upon  pressure.
