AmMi?ch.X.rm'}       Nature  and  Action  of  Toxins.  107 
of  that  species  of  animals,  the  injection  of  rabbit's  milk  into  a  rabbit 
would  not  lead  to  a  production  of  a  precipitin. 
The  production  of  toxins  and  antitoxins  through  the  overprolific 
regeneration  of  saturated  side-chains  form  a  plausible  theory  to 
account  for  the  non-toxicity  of  the  sterile  cultures  of  many  bacteria, 
as  those  of  typhoid,  cholera,  etc.  There  can  be  little  doubt  that 
these,  as  well  as  diphtheria  and  tetanus,  act  by  the  production  of 
toxins.  The  absence  of  such  toxins  in  culture  has  been  explained 
by  several  theories  :  It  may  be  assumed  that  the  culture  media  are 
unfit  for  toxin  formation  ;  that  the  toxins  are  very  firmly  bound  in 
the  bacterial  cells,  and  are  only  liberated  on  the  disintegration  of 
these  cells  ;  or  finally,  that  the  toxins  are  only  produced  in  con- 
siderable amount  in  the  contest  of  the  bacteria  with  the  tissue-cells. 
Whilst  there  is  probably  considerable  truth  in  the  first  two  explana- 
tions, the  last  accords  best  with  the  theories  which  we  have  studied. 
It  will  be  recalled  that  toxins  and  antitoxins  do  not  differ  in  their 
nature ;  the  terms  refer  merely  to  the  damage  or  protection  to  man. 
The  biogen  of  the  bacterial  cells  behaves  precisely  like  the  biogen 
of  a  man,  and  from  the  standpoint  of  the  bacterium,  the  terms  of 
toxin  and  antitoxin  are  precisely  reversed.  It  reacts  to  what  we 
call  antitoxin,  but  what  the  bacterium  would  call  toxin,  in  precisely 
the  same  way  in  which  the  human  biogen  would  react — by  the 
increased  production  of  an  antibody.  Let  us  suppose  that  we  intro- 
duce a  colony  of  cholera  spirilla  into  the  circulation  of  an  animal. 
The  biogen  of  these  bacteria  may  be  represented  as 
B  —  R<T 
In  the  culture  medium  these  have  produced  a  small  excess  of  T, 
which  goes  into  solution,  so  little  that  it  cannot  be  demonstrated  by 
ordinary  tests — enough,  however,  to  combine  with  the 
of  some  body-cells  and  lead  to  an  increased  production  of  this  com- 
plex.   This  now  combines  with  the 
;  b-r<t 
