﻿Commissioner 
  of 
  Ageicultuee. 
  515 
  

  

  the 
  germ 
  were 
  indeed 
  a 
  distinct 
  species. 
  Bnt 
  it 
  might 
  well 
  have 
  

   been 
  considered 
  that 
  a 
  microbe 
  which 
  had 
  changed 
  its 
  aptitudeg 
  

   in 
  a 
  given 
  environment 
  conld 
  presumably 
  revert 
  to 
  its 
  original 
  

   habits 
  nnder 
  the 
  incentive 
  of 
  a 
  suitable 
  medium. 
  And 
  this 
  is 
  

   precisely 
  what 
  does 
  take 
  place. 
  Pastenr 
  has 
  shown 
  that 
  the 
  less 
  

   potent 
  rabic 
  vims 
  becomes 
  more 
  potent 
  when 
  passed 
  several 
  times 
  

   through 
  the 
  body 
  of 
  a 
  rabbit, 
  and 
  that 
  the 
  weakened 
  anthrax 
  germ 
  

   acquires 
  greater 
  force 
  when 
  passed 
  through 
  a 
  series 
  of 
  small 
  birds 
  

   or 
  newly-born 
  mammals. 
  

  

  To 
  come 
  to 
  tuberculosis, 
  Tnideau 
  tells 
  us 
  that 
  a 
  culture 
  of 
  

   bacillus 
  tuberculosis 
  from 
  man 
  inoculated 
  on 
  the 
  rabbit, 
  and 
  then 
  

   cultivated 
  for 
  two 
  years 
  in 
  vitro, 
  becomes 
  much 
  less 
  destructive 
  

   to 
  guinea-pigs, 
  and 
  that 
  after 
  six 
  years 
  of 
  such 
  artificial 
  culture 
  

   all 
  the 
  guinea-pigs 
  inoculated 
  with 
  it 
  live 
  for 
  many 
  months, 
  some 
  

   for 
  two 
  and 
  a 
  half 
  vears, 
  and 
  some 
  even 
  recover. 
  The 
  usual 
  life 
  

   of 
  the 
  guinea-pig 
  after 
  inoculation 
  is 
  seventeen 
  days.^ 
  All 
  of 
  our 
  

   zymotic 
  diseases 
  have 
  in 
  a 
  similar 
  way 
  cycles 
  of 
  malignancy 
  and 
  

   benignancy. 
  For 
  a 
  series 
  of 
  years 
  measles, 
  scarlatina, 
  diphtheria, 
  

   smalljwx, 
  or 
  grippe 
  have 
  an 
  unwonted 
  mildness, 
  and, 
  again, 
  one 
  or 
  

   another 
  merges 
  into 
  a 
  cycle 
  of 
  extreme 
  and 
  fatal 
  maligTiancy. 
  

   Rinderpest 
  on 
  tlie 
  steppes 
  of 
  Asia 
  is 
  comparatively 
  harmless 
  to 
  

   the 
  native 
  stock, 
  l)ut 
  among 
  outside 
  cattle 
  imported 
  into 
  the 
  steppes 
  

   or 
  attacked 
  in 
  their 
  native 
  lands 
  it 
  is 
  habitually 
  fatal. 
  Texas 
  

   fe^^er 
  is 
  mild 
  among 
  cattle 
  in 
  the 
  Gulf 
  States, 
  but 
  very 
  deadly 
  to 
  

   Korthern 
  stock. 
  Glanders 
  is 
  not 
  at 
  all 
  fatal 
  to 
  horses 
  of 
  the 
  

   plains, 
  the 
  Rockies, 
  or 
  the 
  Sierras; 
  but 
  it 
  becomes 
  redoubtable 
  

   when 
  these 
  horses 
  cany 
  it 
  to 
  the 
  Eastern 
  seaboard, 
  and 
  still 
  more 
  

   so 
  in 
  Western 
  Europe. 
  It 
  is 
  a 
  common 
  experience 
  to 
  see 
  a 
  malady 
  

   transformed 
  through 
  the 
  effects 
  of 
  heredity 
  or 
  acquired 
  immunity, 
  

   through 
  environment 
  or 
  the 
  temporary 
  mitigation 
  of 
  virulence 
  in 
  

   the 
  germ; 
  and 
  again 
  we 
  see 
  the 
  same 
  disease, 
  no 
  longer 
  restrained 
  

   by 
  such 
  inhibitory 
  conditions, 
  bursting 
  forth 
  as 
  a 
  malignant 
  and 
  

   deadly 
  plague. 
  "We 
  have, 
  therefore, 
  no 
  warrant 
  for 
  the 
  hypothesia 
  

  

  1 
  Johns 
  Hopkins 
  Hospital 
  Reports, 
  Bulletin 
  100. 
  

  

  