Am.  Jour.  Pharm. 
May,  1914. 
Autogenous  Vaccines. 
207 
Pasteur,  Koch,  Pfeiffer,  Ehrlich,  Behring,  Wassermann,  Noguchi, 
and  others. 
Bacteria  are  divided  into  two  classes,  the  good  and  the  bad: 
saprophytic  and  pathogenic.  The  saprophytic  bacteria  are  scav- 
engers; they  thrive  best  on  dead  tissues  and  assist  in  freeing  the 
body  of  many  waste  products.  Pathogenic  bacteria  thrive  best  on 
the  living  tissues  of  the  host,  in  whom  they  are  capable  of  producing 
disease.  Their  pathogenic  action  is  due  to  the  liberation  of  the 
toxins  they  contain  or  the  elaboration  of  poisons  in  the  tissues 
of  the  host. 
Of  these  bacterial  toxins  there  are  two  main  types:  The  exo- 
toxins, contained  in  bacteria  whose  poisonous  principles  are  capable 
of  being  dissolved  out  of  the  bacterial  cell.  To  this  class  belong  the 
bacillus  of  diphtheria  and  the  bacillus  of  tetanus.  The  great  ma- 
jority of  bacteria,  however,  produce  endotoxins,  or  poisons  which 
are  incapable  of  separation  from  the  cell  bodies  by  any  of  our 
known  filtration  methods.  Examples  of  this  are  the  bacillus  of 
typhoid  fever  and  the  streptococcic  and  staphylococcic  groups,  etc. 
While  bacteria  are  capable  of  producing  disease,  it  is  not  through 
their  mere  presence  per  se,  for,  as  we  know,  our  persons  in  health 
permit  of  the  culturization  of  numerous  pathogenic  bacteria,  there- 
fore other  factors  must  enter  in,  and  these  factors  comprise  the 
natural  defensive  mechanism  of  the  body  against  disease. 
Natural  Resistance. — This  varies  greatly  with  the  individual 
and  has  a  certain  selective  action,  for  why  is  it  that  one  person 
can  harbor  in  his  mouth  virulent  pneumococci  and  streptococci  and 
yet  can  go  through  life  without  a  single  attack  of  pneumonia,  and, 
conversely,  be  subject  to  repeated  attacks  of  tonsillitis ;  whereas, 
another  individual  harboring  the  same  organisms  may  have  several 
attacks  of  pneumonia  during  his  lifetime,  and  none  of  tonsillitis. 
This  is  due  to  the  development  of  what  we  call  immunity,  which  is 
the  power  of  resistance  the  body  tissues  are  able  to  exert  against 
bacterial  poisons.  Immunity  may  be  divided  into  species  and  racial 
immunity. 
Species  Immunity. — It  is  well  known  that  many  animals  are 
naturally  immune  to  diseases  common  to  man,  and  that  it  is  only 
with  the  greatest  experimental  difficulties  that  infections  with  those 
diseases  can  be  made  successfully. 
Racial  Immunity. — Also,  among  the  different  races  of  the  same 
species  there  appears  to  be  a  natural  immunity  against  certain 
