Am'M^ri9i4 arm' }      Use  of  Antitoxins  and  Vaccines.  201 
For  an  explanation  of  this  phenomenon  we  must  go  back  to  the 
work  of  Prof.  Victor  C.  Vaughan  upon  the  chemistry  of  the 
protein  molecule.  Vaughan  has  shown  that  a  protein,  treated 
chemically  according  to  his  method,  is  split  into  two  parts — the  one 
poisonous,  the  other  non-poisonous.  The  poisonous  part  obtained 
from  all  proteins  is  the  same  whether  it  results  from  the  splitting 
of  egg  white  or  from  the  splitting  of  typhoid  bacilli;  the  symptoms 
leading  to  death  in  the  guinea  pig  are  identical.  This  poisonous 
part,  then,  is  a  poison  and  has  no  other  function  or  effect ;  one  dose 
has  no  bearing  upon  the  effect  of  a  subsequent  dose,  no  hyper- 
susceptibility  is  produced,  and  no  tolerance,  even  by  repeated 
administration. 
The  non-poisonous  part,  on  the  other  hand,  is  specific  in  its 
action.  The  non-poisonous  part  of  typhoid  bacillus  protein  will 
immunize  an  animal  against  typhoid  infection,  but  not  against 
infection  with  colon  bacilli ;  the  non-poisonous  part  of  horse  serum 
will  sensitize  a  guinea  pig  to  horse  serum,  but  not  to  goat  or 
sheep  serum. 
These  results  of  Vaughan's  work  upon  the  chemistry  of  proteins 
suggest  an  explanation  of  the  mechanism  of  anaphylaxis ;  they  show 
us  that,  instead  of  being  the  opposite  of  immunity,  anaphylaxis  is 
merely  one  of  its  manifestations ;  and,  furthermore,  they  give  us  a 
clearer  understanding  of  immunity  itself. 
When  foreign  proteins  are  injected  into  the  tissues  of  an  animal, 
the  body  cells  at  once  set  to  work  to  remove  this  protein.  They 
prepare  a  ferment  capable  of  splitting  the  protein  molecule,  which 
possibly  because  of  its  size  is  not  diffusible,  into  smaller  fractions 
able  to  pass  into  the  circulatory  system  and  be  thence  eliminated. 
These  fractions  of  the  protein  molecule  are  similar  to  those  ob- 
tained by  Vaughan  in  his  chemical  splitting;  that  is,  a  poisonous 
part  which,  after  the  first  injection,  is  liberated  slowly  and  is  there- 
fore harmless  in  its  effect,  and  a  non-poisonous  specific  part  which 
stimulates  the  body  cells  to  produce  a  specific  ferment-like  sub- 
stance. About  two  weeks  after  injection  the  protein  has  been 
entirely  removed  from  the  tissues,  the  poisonous  part  has  been 
eliminated  so  gradually  that  no  symptoms  have  resulted,  and  the 
non-poisonous  part  has  stimulated  the  tissues  to  generate  a  large 
amount  of  specific  protein-splitting  ferment. 
At  this  point  we  must  pause  to  note  that,  according  to  Vaughan, 
the  protein-splitting  ferment  includes  the  antibodies  so  difficult  to 
