While  the  evidence  is  thus  quite  conclusive  that  cells  which  are
susceptible  to  the  toxic  action  of  the  toxin  molecule  may  also  produce
antitoxins,  there  are  other  facts  to  show  that  this  can  also  occur  in
non-sensitive  cells.  If,  however,  by  any  chance  the  sensitive  cells
are  the  only  ones  which  possess  the  necessary  combining  group  for
the  toxin,  they  will  of  necessity  be  the  only  ones  from  which  anti-
toxin formation  can  proceed.  We  have  seen  already  that  in  the
case  of  the  guinea-pig  the  nerve  tissue  is  the  only  tissue  which  can


122  THE  SIDE-CHAIN  THEORY

exercise  a  detoxifying  action.  In  the  case  of  the  rabbit,  on  the  other
hand,  such  an  effect  can  be  produced  not  only  by  the  cells  of  the
nervous  system,  but  also  by  the  liver  and  the  spleen.  If,  moreover,
a  guinea-pig  is  injected  with  tetanus  toxin  the  fatal  dose  is  the
same,  no  matter  whether  the  poison  is  injected  intracerebrally,
intravenously,  or  subcutaneously.  In  the  rabbit  the  result  is  dif-
ferent. Intracerebral  injection  of  tiny  doses  readily  leads  to  fatal
tetanus,  while  much  larger  amounts  can  be  administered  sub-
cutaneously without  causing  a  fatal  result,  particularly  if  the  larger
nerve  trunks  in  the  district  in  which  the  injection  is  made  are
previously  cut.  As  abundant  antitoxin  formation  then  takes  place
notwithstanding  the  fact  that  the  access  of  the  toxin  to  the  brain
has  been  excluded  so  far  as  possible,  the  inference,  of  course,  is
perfectly  warrantable  that  the  antitoxin  in  question  is  largely
produced  by  cells  which  are  not  susceptible  to  the  toxic  action
of  the  poison.
The  same  point  is  also  well  illustrated  in  the  case  of  the  alligator.
This  animal  is  not  at  all  susceptible  to  the  action  of  tetanus  poison.
