﻿FILTKABLE 
  VIRUSES 
  — 
  BOYCOTT 
  • 
  335 
  

  

  culture 
  of 
  the 
  Rous 
  agent 
  — 
  indeed 
  all 
  the 
  evidence 
  we 
  have 
  is 
  con- 
  

   clusive 
  on 
  that 
  point. 
  Viruses 
  are 
  certainly 
  not 
  enzymes. 
  Apart 
  

   from 
  living 
  cells 
  they 
  may 
  for 
  a 
  long 
  time 
  survive, 
  i. 
  e., 
  remain 
  in 
  

   such 
  a 
  state 
  that, 
  on 
  altering 
  the 
  conditions, 
  they 
  can 
  give 
  rise 
  to 
  their 
  

   characteristic 
  effect 
  — 
  vaccinia, 
  a 
  sarcoma, 
  bacteriolysis, 
  etc. 
  But 
  

   there 
  is 
  no 
  evidence 
  that 
  they 
  multiply 
  under 
  these 
  conditions, 
  and 
  

   multiplication 
  at 
  the 
  expense 
  of 
  the 
  environment 
  is 
  probably 
  regarded 
  

   by 
  most 
  of 
  us 
  as 
  the 
  most 
  important 
  criterion 
  of 
  life. 
  

  

  For 
  their 
  multiplication, 
  young 
  growing 
  cells 
  are 
  especially 
  suitable, 
  

   and 
  it 
  may 
  be 
  quite 
  necessary. 
  The 
  bacteriophage 
  multiplies 
  only 
  

   with 
  the 
  multiplication 
  of 
  the 
  associated 
  bacteria, 
  and 
  vaccinia, 
  

   herpes, 
  Rous 
  sarcoma, 
  etc., 
  develop 
  and 
  multiply 
  especially 
  in 
  con- 
  

   nection 
  with 
  the 
  growth 
  of 
  cells 
  which 
  results 
  from 
  local 
  injury. 
  

   Cell 
  injury 
  and 
  cell 
  growth 
  are 
  so 
  intimately 
  related 
  that 
  I 
  know 
  of 
  no 
  

   case 
  where 
  cell 
  growth 
  can 
  certainly 
  be 
  excluded, 
  but 
  at 
  present 
  we 
  

   can 
  not 
  be 
  quite 
  certain 
  that 
  it 
  is 
  necessary. 
  It 
  seems 
  also 
  to 
  be 
  true 
  

   that 
  viruses 
  multiply 
  only 
  in 
  the 
  course 
  of 
  the 
  production 
  of 
  their 
  

   specific 
  effect. 
  

  

  But 
  though 
  the 
  fact 
  of 
  multiplication 
  is 
  plain, 
  it 
  is 
  by 
  no 
  means 
  

   proved 
  that 
  it 
  is 
  effected 
  in 
  the 
  w^ay 
  which 
  is 
  familiar 
  in 
  bacteria 
  and 
  

   living 
  organisms 
  generally. 
  We 
  put 
  in 
  so 
  much 
  virus 
  and 
  we 
  get 
  out 
  

   more: 
  We 
  have 
  no 
  evidence, 
  nor, 
  I 
  think, 
  the 
  right 
  to 
  assume, 
  that 
  

   the 
  particles 
  which 
  we 
  get 
  out 
  are 
  the 
  direct 
  descendants 
  of 
  those 
  

   we 
  put 
  in. 
  

  

  It 
  may 
  be 
  that 
  these 
  facts 
  are 
  best 
  explained 
  bj^ 
  supposing 
  that 
  

   viruses 
  are 
  obligatory 
  intracellular 
  parasites, 
  and 
  that 
  the 
  difficulty 
  

   of 
  cultivating 
  them 
  on 
  artificial 
  media 
  will 
  be 
  solved 
  when 
  we 
  can 
  

   imitate 
  sufficiently 
  closely 
  the 
  essential 
  features 
  of 
  the 
  intracellular 
  

   environment; 
  pathogenic 
  protozoa 
  were 
  not 
  cultivated 
  at 
  the 
  first 
  

   trial. 
  Very 
  few 
  bacteria 
  live 
  inside 
  animal 
  cells, 
  and 
  it 
  is 
  perhaps 
  

   significant 
  that 
  those 
  that 
  do 
  (e. 
  g., 
  Brucella 
  abortus 
  and 
  Bacteriujn 
  

   tularense) 
  are 
  among 
  the 
  smallest 
  of 
  the 
  group. 
  Viruses 
  have, 
  of 
  

   course, 
  not 
  been 
  seen 
  inside 
  cells, 
  but 
  their 
  dependence 
  on 
  living 
  cells, 
  

   and 
  the 
  considerable 
  regularity 
  with 
  which 
  their 
  presence 
  is 
  indicated 
  

   by 
  cytoplasmic 
  and 
  intranuclear 
  ''bodies" 
  (some 
  of 
  them 
  of 
  specifi- 
  

   cally 
  characteristic 
  appearances) 
  make 
  it 
  quite 
  likely 
  that 
  such 
  a 
  

   position 
  is 
  their 
  natural 
  habitat, 
  in 
  which 
  they 
  multiply 
  and 
  from 
  

   which 
  they 
  spread, 
  as 
  they 
  do, 
  to 
  other 
  places, 
  liquids, 
  and 
  secretions. 
  

   This 
  habitat 
  might 
  have 
  something 
  to 
  do 
  with 
  the 
  peculiarities 
  of 
  

   their 
  immunological 
  relations. 
  Living 
  within 
  cells 
  it 
  is 
  perhaps 
  

   unnecessary 
  for 
  them 
  to 
  produce 
  any 
  definite 
  toxins; 
  mechanical 
  

   disorganization 
  of 
  the 
  cellular 
  anatomy 
  might 
  well 
  be 
  the 
  effective 
  

   cause 
  of 
  the 
  injuries 
  they 
  produce. 
  The 
  general 
  symptoms 
  of 
  infec- 
  

   tions 
  (headache, 
  fever, 
  prostration) 
  are 
  caused, 
  as 
  in 
  bacterial 
  infec- 
  

   tions, 
  mostly 
  by 
  substances 
  derived 
  from 
  the 
  injured 
  cells 
  of 
  the 
  host, 
  

  

  