INFECTION  BY  AIR  289

tuberculosis,  may,  when  dry,  retain  their  vitality  for  months.
In  addition  to  the  general  knowledge  of  the  resisting  power  of
bacteria,  which  has  been  accumulating,  special  and  systematic
attempts  have  been  made  to  determine  directly  the  chances
of  infection  by  air-borne  dust.
Studies  on  the  Drying  of  Germs.  —  Among  the  earliest
work  of  this  kind  was  that  by  Germano.1  He  employed  room
dust  and  different  kinds  of  earth,  which  after  sterilization
were  inoculated  with  cultures  of  bacteria  grown  in  various
media.  He  found  that  generally  the  bacteria  perished  sooner
in  room  dust  than  in  other  materials,  and  that  bacteria
which,  like  the  typhoid  bacillus,  might  survive  for  months
even  when  dried  on  clothing  or  solid  material,  would  speedily
die  in  a  very  short  time  in  dust.  After  a  large  number  of
experiments  he  concluded  that  cholera,  plague,  typhoid  fever,
influenza  and  gonorrhea  could  not  be  dust-borne;  that  under
certain  circumstances,  with  strong  air  currents,  streptococcus
and  the  germs  of  pneumonia  and  of  diphtheria  might  be  air-
borne, and  that,  besides  the  spores  of  anthrax  and  tetanus,
many  of  the  pus  organisms,  meningococcus  and  the  tubercle
bacillus,  might  be  transported  in  dust.  It  is  suspected  that
he  did  not  employ  the  true  coccus  of  cerebro-spinal  meningi-
tis, for  recent  workers  are  agreed  that  this  bacterium  has  very
weak  powers  of  resistance.  His  results  with  the  pneumo-
coccus  also  are  surprising,  as  this  too  is  rather  feeble.
