200  Use  of  Antitoxins  and  Vaccines.       j Am •MJa°yur*19i^ arm' 
inject  a  corresponding  quantity  of  a  harmless  alkali.  The  acid  is 
neutralized,  the  disease  is  controlled,  and  the  fate  of  the  patient 
now  depends  only  upon  the  amount  of  damage  done  to  the  tissues 
before  the  alkali  was  administered. 
In  tetanus  the  case  is  slightly  different.  Tetanus  toxin  has  a 
strong  affinity  for  the  nerve  tissues,  and  the  compound  formed  by 
this  union  cannot  be  split  up  by  antitoxin.  After  symptoms  of  the 
disease  have  developed,  there  is  but  one  hope  in  treating  tetanus 
with  antitoxin.  If  treatment  has  begun  before  the  lethal  quantity 
of  toxin  has  been  fixed  by  the  nervous  tissue,  and  if  the  amount  of 
antitoxin  then  administered  be  sufficient  to  neutralize  the  free  toxin 
in  the  blood,  there  is  a  chance  that  recovery  may  ensue. 
Bacterial  Vaccines. 
For  a  clear  understanding  of  the  action  of  bacterial  vaccines, 
it  may  be  helpful  to  consider  this  subject  from  the  standpoint  of 
our  knowledge  of  anaphylaxis.  Anaphylaxis,  in  its  derivation, 
means  a  lack  of  resistance — it  is  the  opposite  of  prophylaxis.  Richet, 
in  his  investigation  of  certain  poisons  derived  from  sea  urchins, 
noted  that  an  injection  of  this  poison  into  a  dog,  instead  of  render- 
ing the  animal  immune  to  a  second  dose,  actually  made  him  more 
susceptible.  The  work  of  Rosenau  and  Anderson  showed  still  more 
clearly  the  operation  of  this  phenomenon. 
Anaphylaxis  concerns  the  effect  of  proteins  or  albuminous  sub- 
stances upon  animals ;  it  concerns  all  proteins,  whether  they  are 
poisonous  in  themselves  or  not ;  for  instance,  egg  white  and  normal 
horse  serum  act  precisely  as  the  proteins  of  the  plague  bacillus  or 
of  the  typhoid  bacillus.  And,  furthermore,  the  proteins  of  dead 
bacteria  act  practically  in  the  same  way  as  the  proteins  of  living 
bacteria.  It  must  be  remembered,  however,  that  anaphylactic 
symptoms  can  be  produced  only  by  proteins  foreign  to  the  animal ; 
that  is,  anaphylaxis  cannot  occur  in  a  guinea  pig  from  the  repeated 
injection  of  guinea-pig  serum,  nor  can  the  symptoms  be  produced 
in  a  horse  by  the  injection  of  horse  serum. 
If  we  inject  a  guinea  pig  parenterally — that  is,  by  any  route 
except  by  the  gastro-intestinal  canal — it  does  not  appear  to  suffer 
the  slightest  inconvenience.  If,  however,  we  inject  this  animal,  two 
or  more  weeks  later,  with  the  same  protein,  it  will  die  within  one 
or  two  minutes  and  with  very  definite  symptoms  accompanying 
death.    This  is  a  manifestation  of  anaphylaxis. 
