104  Nature  and  Action  of  Toxins.        { A Va™h,  ^_rra- 
are  quickly  broken  down  again,  the  receptor  again  becoming  unsatu- 
rated; but  if  a  receptor  is  saturated  by  a  molecule  which  does  not 
break  down  again,  that  receptor  is  lost  to  the  biogen.  This  seems 
to  happen  when  the  reagent  is  a  toxin. 
We  have  seen  that  a  complex  molecule  takes  up  other  molecules 
only  into  its  side-chains.  The  same  fact  may  be  stated  in  other 
words:  a  complex  molecule  does  not  unite  with  another  molecule 
except  by  its  side-chain.  A  potentially  toxic  molecule  often  cannot 
act  upon  biogen,  because  it  has  no  appropriate  side-chain  by  which 
it  can  enter  into  a  biogen  combination.  If  now  such  a  side-chain  is 
introduced,  the  possibility  of  combination,  and  thereby  of  action,  is 
given.  For  instance,  C6H6  has  potentially  the  toxicity  of  the  coal- 
tar  antiseptics ;  but  having  no  affinity  for  biogen  it  cannot  exert  its 
action.  Hydroxyl  OH  has  considerable  of  this  affinity,  but  its  action 
is  quite  weak,  and  totally  unlike  that  of  the  coal-tar  series.  If  the 
OH  is  introduced  into  the  C6H6 — producing  carbolic  acid — we  obtain 
at  once  a  great  toxic  and  antiseptic  action,  because  now  the  benzol 
molecule  can  unite  with  the  biogen  molecule  through  the  inter- 
mediation of  the  OH.  To  anticipate  the  terminology  of  toxins :  C6H- 
is  the  toxic  complement ;  OH  is  the  intermediary  body.1  Now,  in 
the  case  of  toxin  action,  both  classes  of  constituents  must  be  present — 
a  toxic  complement  which  contains  the  potential  toxic  action,  and 
an  intermediary  body  which  is  necessary  to  bring  this  potential 
action  into  execution ;  and  besides  these  there  must  be  a  fitting 
receptor  or  side-chain  in  the  biogen  to  which  they  may  attach  them- 
selves. A  very  great  diversity  exists  as  to  the  source  of  the  first 
two  components.  The  foreign  toxin  may  contain  both  the  toxic 
complement  and  the  intermediary  body ;  or,  it  may  contain  either 
the  toxic  complement  or  the  intermediary  body  alone,  the  other 
ingredient  being  furnished  by  the  biogen,  or  from  some  other 
extraneous  source,  as,  for  instance,  by  the  serum  in  cases  in  which 
the  toxic  action  is  on  the  blood-corpuscles. 
1To  illustrate  or  emphasize  certain  features  of  the  hypotheses,  a  large  num-' 
ber  of  nearly  equivalent  terms  are  commonly  used.  These  often  differ  a  shade 
amongst  themselves;  but  as  their  meaning  has  altered  somewhat  with  the  evo- 
lution of  the  theory,  and  as  they  are  often  rather  loosely  interchanged,  they  are 
apt  to  give  rise  to  much  confusion.    These  synonyms  are: 
Receptor. — Haptophor,  side-chain,  amboceptor. 
Toxic  Complement. — Complement,  alexin,  cytase. 
Intermediary  Body. — Toxiphor,  immunizer,  sensitizer,  fixative,  preparative, 
copula,  desmon,  toxoid,  amboceptor. 
