A.m.  Jour.  Pliarm. 
July,  1891. 
Germs  and  Disease. 
363 
Chief  among  the  organisms  visible  in  the  drop  of  meat  infusion 
are  numbers  of  rod-shaped  bodies  vibrating  in  a  most  characteristic 
manner.  These  are  the  lowest  forms  of  plant  life,  being  composed 
of  a  single  cell  and  reproducing  their  kind  by  simple  division  of 
their  bodies.  They  are  known  to  naturalists  as  bacteria.  Among 
these  microscopic  plants  we  have  as  much  divergence  in  form  and 
properties  as  can  be  found  among  the  higher  plants  that  people  our 
fields  and  lanes  and  gardens.  The  remarkable  difference  in  proper- 
ties characterizing  some  of  the  latter  which  so  closely  resemble 
each  other  in  form  as  to  be  placed  by  botanists  in  the  same  order 
is  a  fact  now  generally  recognized.  Thus,  we  have  such  a  poisonous 
plant  as  Belladonna,  or  "  deadly  nightshade,"  belonging  to  the  same 
order  as  the  potato  and  scarcely  distinguishable  from  it  by  the 
untrained  eye ;  the  hemlock,  too,  claims  as  close  relations  to  the  carrot, 
the  parsley,  the  caraway  and  the  coriander.  The  bacteria  found  in 
infusions  of  hay  and  of  meat  correspond  to  the  useful  plants,  for 
besides  being  in  themselves  harmless,  they  act  as  nature's  scaven- 
gers by  feeding  on  and  converting  into  its  component  elements  the 
putrefying  matter  among  which  they  live.  Corresponding  to  the 
poisonous  plants,  we  have  the  bacteria  which  are  the  essential 
factors  in  the  production  of  infectious  diseases  and  popularly  known 
as  "  disease  germs." 
The  "  germ  theory"  of  disease  is  not  a  product  of  to-day,  but 
was  mooted  as  long  ago  as  1675.  Since  that  time  it  has  passed 
through  many  phases,  and  been  to  all  appearances  as  completely 
proved  as  it  has  afterwards  been  disproved.  The  "  snow-white  cube 
of  truth,"  of  which  all  the  theories  have  been  mere  vestments, 
still  survives,  however,  and  its  recognition  has  been  rendered  cer- 
tain by  the  more  accurate  methods  of  research  and  the  more  per- 
fect instruments  brought  to  bear  on  its  numerous  manifestations 
within  recent  years.  Since  the  discovery  by  Pasteur — fully  twenty 
years  ago — that  a  disease  which  caused  great  ravages  among  silk 
worms  in  France  was  caused  by  a  micro-organism,  progress  has 
been  continuous.  In  1877,  Koch  published  the  result  of  his 
researches  on  the  life  history  of  the  bacillus — a  species  of  Bacterium 
— of  splenic  fever.  His  observations  were  confirmed  by  Pasteur, 
who  also  showed  how  the  bacillus  might  be  weakened  or  "  attenu- 
ated," so  that  inoculation  with  the  attenuated  form  prevented  or 
mitigated  the  more  virulent  disease.    These  researches  laid  the 
