ASvSbe^SS?-}  Antitoxins.  ■  613 
in  diphtheria  itself  the  special  bacillus,  which  was  shown  by  Lbffler 
to  be  its  cause,  does  not  become  propagated  in  the  blood,  like  the 
microbe  of  chicken  cholera,  but  remains  confined  to  the  surface  on 
which  it  first  appeared ;  but  the  toxin  which  it  secretes  is  absorbed 
from  that  surface  into  the  blood,  and  so  poisons  the  system.  Simi- 
lar observations  have  been  made  with  regard  to  the  microbes  of 
some  other  diseases,  as,  for  example,  the  bacillus  of  tetanus,  or  lock- 
jaw. This  remains  localized  in  the  wound,  but  forms  a  special  toxin 
of  extreme  potency,  which  becomes  absorbed  and  diffused  through 
the  body. 
Wonderful  as  it  seems,  each  poisonous  microbe  appears  to  form 
its  own  peculiar  toxin.  Koch's  tuberculin  was  of  this  nature,  a  pro- 
duct of  the  growth  of  the  tubercle  bacillus  in  culture  media.  Here 
again,  great  effects  were  produced  by  extremely  minute  quantities 
of  the  substance;  but  here  a  new  peculiarity  showed  itself,  viz.:  that 
patients  affected  with  tubercular  disease,  in  any  of  its  varied  forms, 
exhibited  inflammation  in  the  affected  part,  and  general  fever  after 
receiving  under  the  skin  an  amount  of  the  material  which  had  no 
effect  whatever  upon  healthy  persons.  I  witnessed  in  Berlin  some 
instances  of  these  effects,  which  were  simply  astounding.  Patients 
affected  with  a  peculiar  form  of  obstinate  ulcer  of  the  face  showed, 
after  a  single  injection  of  the  tuberculin,  violent  inflammatory  red- 
ness and  swelling  of  the  sore  and  surrounding  skin ;  and,  what  was 
equally  surprising,  when  this  disturbance  subsided  the  disease  was 
found  to  have  undergone  great  improvement.  By  repetition  of  such 
procedures,  ulcers,  which  had  been  steadily  advancing  in  spite  of 
ordinary  treatment,  became  greatly  reduced  in  size  and,  in  some 
instances,  apparently  cured.  Such  results  led  Koch  to  believe  that 
he  had  obtained  an  effectual  means  of  dealing  with  tubercular  dis- 
ease in  all  its  forms.  Unhappily  the  apparent  cure  proved  to  be 
only  of  transient  duration,  and  the  high  hopes  which  had  been 
inspired  by  Koch's  great  reputation  were  dashed.  It  is  but  fair  to 
say  that  he  was  strongly  urged  to  publish  before  he  was  himself 
disposed  to  do  so,  and  we  cannot  but  regret  that  he  yielded  to  the 
pressure  put  upon  him. 
But,  though  Koch's  sanguine  anticipations  were  not  realized,  it 
would  be  a  great  mistake  to  suppose  that  his  labors  with  tuberculin 
have  been  fruitless.  Cattle  are  liable  to  tubercle  and,when  affected  with 
it,  may  become  a  very  serious  source  of  infection  for  human  beings, 
