﻿FILTRABLE 
  VIRUSES 
  — 
  BOYCOTT 
  337 
  

  

  from 
  the 
  bodies 
  of 
  the 
  bacilli, 
  and 
  impossible 
  to 
  investigate 
  them 
  in 
  

   detail. 
  Nor 
  should 
  we, 
  I 
  think, 
  be 
  too 
  shy 
  of 
  drawing 
  general 
  con- 
  

   clusions 
  from 
  such 
  specially 
  easy 
  and 
  demonstrative 
  examples 
  as 
  

   Providence 
  has 
  provided 
  for 
  our 
  learning 
  and 
  pushes 
  under 
  our 
  noses, 
  

   till 
  even 
  our 
  stupidity 
  is 
  bound 
  to 
  take 
  notice; 
  diphtheria 
  and 
  tetanus 
  

   for 
  toxins, 
  the 
  guinea 
  pig's 
  peculiar 
  bronchial 
  musculature 
  for 
  ana- 
  

   phylaxis, 
  mice 
  and 
  tar 
  for 
  tumors, 
  radium 
  are 
  such 
  signposts; 
  the 
  

   Rous 
  tumor 
  is 
  another. 
  

  

  Another 
  analogous 
  phenomenon 
  takes 
  us, 
  I 
  think, 
  a 
  step 
  further. 
  

   The 
  products 
  of 
  autolysis 
  of 
  dead 
  cells 
  in 
  the 
  body, 
  in 
  suitable 
  con- 
  

   centration, 
  stimulate 
  tissue 
  growth. 
  It 
  is 
  a 
  beautiful 
  self-regulating 
  

   mechanism 
  in 
  which 
  the 
  amount 
  of 
  stimulus 
  is 
  proportionate 
  to 
  the 
  

   amount 
  of 
  cell 
  destruction, 
  and 
  therefore 
  to 
  the 
  amount 
  of 
  cell 
  growth 
  

   required, 
  and 
  it 
  is 
  obviously 
  of 
  the 
  highest 
  importance 
  for 
  survival 
  — 
  

   a 
  far 
  more 
  potent 
  factor 
  in 
  selection 
  and 
  evolution 
  than 
  any 
  disease 
  

   has 
  ever 
  been. 
  As 
  it 
  normally 
  operates 
  in 
  healing 
  our 
  cut 
  fingers, 
  

   the 
  final 
  result 
  is 
  simply 
  the 
  restoration 
  of 
  the 
  cells 
  which 
  were 
  de- 
  

   stroyed. 
  But 
  if 
  the 
  normal 
  restraint 
  exercised 
  by 
  neighboring 
  tissues 
  

   is 
  evaded 
  and 
  use 
  made 
  of 
  tissue 
  cultures, 
  the 
  products 
  of 
  autolysis 
  

   or 
  metabolism 
  (in 
  the 
  form 
  of 
  extracts 
  of 
  tissues, 
  tumors, 
  or 
  embryos) 
  

   stimulate 
  growth 
  indefinitely 
  and 
  a 
  much 
  larger 
  quantity 
  of 
  tissue 
  

   may 
  be 
  obtained 
  than 
  we 
  started 
  with. 
  From 
  the 
  autolysis 
  of 
  this 
  a 
  

   larger 
  amount 
  of 
  stimulating 
  substance 
  may 
  be 
  obtained, 
  and 
  there 
  

   seems 
  no 
  reason 
  why 
  this 
  process 
  of 
  multiplication 
  should 
  have 
  any 
  

   limit. 
  Normal 
  tissues 
  in 
  the 
  physical 
  isolation 
  of 
  tissue 
  cultures 
  are 
  as 
  

   immortal 
  as 
  malignant 
  tissues 
  in 
  their 
  physiological 
  isolation 
  from 
  the 
  

   rest 
  of 
  the 
  body. 
  

  

  No 
  one 
  would, 
  I 
  think, 
  pretend 
  that 
  these 
  products 
  of 
  autolysis 
  

   are 
  alive 
  in 
  any 
  ordinary 
  sense 
  of 
  the 
  word. 
  They 
  have 
  not 
  received 
  

   nearly 
  as 
  much 
  attention 
  as 
  they 
  deserve, 
  but 
  they 
  are 
  probably 
  of 
  

   relatively 
  simple 
  and 
  discoverable 
  constitutions. 
  Yet 
  applied 
  to 
  cells 
  

   they 
  cause 
  growth, 
  and 
  in 
  so 
  doing 
  potentially 
  increase 
  their 
  own 
  

   quantity; 
  this 
  is 
  very 
  much 
  what 
  the 
  Rous 
  agent 
  does. 
  There 
  are, 
  

   too, 
  these 
  further 
  minor 
  similarities: 
  The 
  Rous 
  agent 
  stimulates 
  one 
  

   particular 
  type 
  of 
  cell 
  (white 
  fibrous 
  connective 
  tissue) 
  to 
  malignancy, 
  

   some 
  extracts 
  of 
  normal 
  tissues 
  stimulate 
  fibroblasts 
  in 
  tissue 
  culture 
  

   while 
  others 
  act 
  specially 
  in 
  epithelial 
  cells; 
  the 
  activity 
  of 
  the 
  Rous 
  

   agent 
  may 
  be 
  encouraged 
  or 
  depressed 
  by 
  the 
  simultaneous 
  presence 
  

   of 
  other 
  tissue 
  extracts, 
  some 
  tissue 
  extracts 
  inhibit 
  growth 
  instead 
  of 
  

   encouraging 
  it. 
  

  

  But 
  the 
  chief 
  importance 
  of 
  the 
  analogy 
  is, 
  I 
  think, 
  in 
  throwing 
  

   light 
  on 
  the 
  nature 
  and 
  origin 
  of 
  the 
  Rous 
  virus. 
  If 
  we 
  agree 
  to 
  put 
  

   the 
  products 
  of 
  autolysis 
  in 
  the 
  category 
  "dead," 
  by 
  what 
  difference 
  

   are 
  we 
  to 
  separate 
  the 
  Rous 
  virus 
  as 
  being 
  "alive"? 
  It 
  can 
  not 
  be 
  

  

  