6i4>  Antitoxins.  {tSS^ 
more  especially  when  the  disease  affects  the  udders  of  cows  and  so 
contaminates  the  milk.  By  virtue  of  the  close  affinity  that  prevails 
between  the  lower  animals  and  ourselves,  in  disease  as  well  as  in 
health,  tuberculin  produces  fever  in  tubercular  cows,  in  doses  which 
do  not  affect  healthy  beasts.  Thus,  by  the  subcutaneous  use  of  a 
little  of  the  fluid,  tubercle  latent  in  internal  organs  of  an  apparently 
healthy  cow  can  be  with  certainty  revealed,  and  the  slaughter  of 
the  animal  after  this  discovery  protects  man  from  infection. 
It  has  been  ascertained  that  glanders  presents  a  precise  analogy 
with  tubercle  as  regards  the  effects  of  its  toxic  products.  If  the 
microbe  which  has  been  found  to  be  the  cause  of  this  disease  is  culti- 
vated in  appropriate  media,  it  produces  a  poison  which  has  received 
the  name  of  mallein ;  and  the  subcutaneous  injection  of  a  suitable 
dose  of  this  fluid  into  a  glandered  horse  causes  striking  febrile 
symptoms,  which  do  not  occur  in  a  healthy  animal.  Glanders,  like 
tubercle,  may  exist  in  insidious,  latent  forms,  which  there  was  for- 
merly no  means  of  detecting,  but  which  are  at  once  disclosed  by 
this  means.  If  a  glandered  horse  has  been  accidentally  introduced 
into  a  large  stable,  this  method  of  diagnosis  surely  tells  whether  it 
has  infected  others.  All  receive  a  little  mallein.  Those  which  be- 
come affected  with  fever  are  slaughtered,  and  thus,  not  only  is  the 
disease  prevented  from  spreading  to  other  horses,  but  the  grooms 
are  protected  from  a  mortal  disorder. 
This  valuable  resource  sprang  from  Koch's  work  on  tuberculin, 
which  has  also  indirectly  done  good  in  other  ways.  His  distin- 
guished pupil,  Behring,  has  expressly  attributed  to  those  researches 
the  inspiration  of  the  work  which  led  him  and  his  since  famous  col- 
laborates, the  Japanese,  Kitasato,  to  their  surprising  discovery  of 
antitoxic  serum.  They  found  that  if  an  animal  of  a  species  liable 
to  diphtheria  or  tetanus  received  a  quantity  of  the  respective  toxin, 
so  small  as  to  be  harmless,  and  afterwards,  at  suitable  intervals,  suc- 
cessively stronger  and  stronger  doses,  the  creature,  in  course  of 
time,  acquired  such  a  tolerance  for  the  poison  as  to  be  able  to 
receive  with  impunity  a  quantity  very  much  greater  than  would  at 
the  outset  have  proved  fatal.  So  far,  we  have  nothing  more  than 
seems  to  correspond  with  the  effects  of  the  increasingly  potent  cords 
in  Pasteur's  treatment  of  rabies.  But  what  was  entirely  new  in 
their  results  was  that,  if  blood  was  drawn  from  an  animal  which  had 
acquired  this  high  degree  of  artificial  immunity,  and  some  of  the  clear 
