^  May  ri9i4arm* }       Use  °f  Antitoxins  and  Vaccines.  205 
selves.  The  autolysate  contains  a  toxic  substance  which  causes 
the  production  of  some  antitoxin.  This  serum,  like  antidysenteric 
serum,  partakes,  therefore,  of  the  nature  of  both  an  antitoxic  and 
an  antibacterial  serum. 
These  serums  depend  for  their  activity  upon  substances  called 
ferments  by  Vaughan,  but,  according  to  the  nomenclature  of  Ehrlich, 
"  antibodies  " ;  that  is,  substances  antagonistic  to  the  bacteria.  Used 
in  sufficiently  large  doses,  antibacterial  serums  have  undoubtedly 
great  value.  The  chief  difficulty  lies  in  the  fact  that  no  method 
has  so  far  been  found  by  which  antibacterial  serums  can  be  pro- 
duced comparable  in  potency  with  diphtheria  antitoxin. 
It  is  well  known  that  a  much  larger  dose  of  any  curative  serum 
must  be  used  if  it  is  injected  subcutaneously  than  if  injected  intra- 
venously. Realizing  this  fact  and  the  relative  weakness  of  anti- 
bacterial serums,  there  is  but  little  doubt  that  their  use  intravenously 
will  be  resorted  to  in  the  future  with  increasing  frequency. 
Summary. 
1.  There  are  two  classes  of  bacteria  with  regard  to  their  method 
of  producing  disease:  (a)  Those  that  produce  soluble  and  diffusible 
toxins,  and  (b)  those  that  do  not. 
2.  The  toxin-producing  bacteria  are  the  diphtheria  bacillus  and 
the  tetanus  bacillus. 
3.  Antitoxins  produced  by  injecting  horses  with  the  specific 
toxins  are  antagonistic  to  the  specific  toxic  products  of  the  bacilli 
in  a  manner  very  similar  to  the  antagonism  between  acid  and  alkali. 
4.  To  the  second  class  belong  the  great  majority  of  the  disease- 
producing  bacteria. 
5.  The  symptoms  in  the  diseases  caused  by  the  latter  are  prob- 
ably the  result  of  the  action  of  their  specific  metabolic  products 
combined  with  the  effect  of  the  liberated  poisonous  part  of  their 
protein  molecule. 
6.  Recovery  from  such  infectious  diseases  depends  upon  the 
production  of  sufficient  specific  protein-splitting  ferment  to  remove 
their  causative  bacteria  from  the  tissues. 
7.  The  amount  of  this  specific  protein-splitting  ferment  may  be 
increased  by  injecting  bacteria  of  the  same  kind  beneath  the  healthy 
skin. 
8.  Immunity  from  infectious  disease  depends  upon  the  existence 
