﻿102 
  

  

  pillars 
  on 
  caterpillar 
  and 
  other 
  nutrient 
  media 
  remained 
  sterile. 
  If 
  

   serial 
  sections 
  are 
  made 
  of 
  diseased 
  caterpillars 
  obtained 
  in 
  the 
  field, 
  

   polyhedral 
  bodies 
  will 
  be 
  found 
  in 
  abundance, 
  but 
  no 
  bacteria 
  in 
  the 
  

   tissues, 
  and 
  usually 
  the 
  intestinal 
  lumen 
  will 
  be 
  free 
  from 
  micro- 
  

   organisms 
  in 
  general. 
  

  

  Great 
  care 
  was 
  taken 
  to 
  procure 
  healthy 
  uninfected 
  caterpillars 
  for 
  

   the 
  experiments, 
  by 
  collecting 
  from 
  localities 
  where 
  no 
  epidemic 
  was 
  

   evident. 
  The 
  caterpillars 
  were 
  divided 
  into 
  groups, 
  and 
  each 
  group 
  

   was 
  subjected 
  to 
  slightly 
  different 
  conditions 
  of 
  temperature, 
  light, 
  

   moisture, 
  etc. 
  This 
  gave 
  the 
  disease, 
  if 
  latent, 
  every 
  chance 
  of 
  becom- 
  

   ing 
  manifest, 
  since 
  conditions 
  unfavourable 
  to 
  the 
  caterpillars 
  are 
  

   believed 
  to 
  assist 
  its 
  development. 
  If 
  the 
  disease 
  under 
  one 
  or 
  other 
  of 
  

   the 
  conditions 
  broke 
  out, 
  the 
  whole 
  of 
  the 
  caterpillars 
  collected 
  from 
  

   the 
  same 
  locality 
  w^ere 
  discarded. 
  Such 
  a 
  method 
  of 
  obtaining 
  healthy 
  

   individuals 
  is 
  much 
  more 
  satisfactory 
  than 
  the 
  blood 
  test, 
  as 
  the 
  

   controls 
  showed. 
  

  

  Many 
  views 
  have 
  been 
  held 
  regarding 
  the 
  agents 
  responsible 
  for 
  the 
  

   disease. 
  Escherich 
  and 
  Miyajima 
  in 
  1911 
  were 
  of 
  the 
  opinion 
  that 
  

   the 
  polyhedral 
  bodies 
  were 
  the 
  carriers 
  of 
  the 
  virus 
  ; 
  Bolle 
  believed 
  

   that 
  a 
  Microsporidian 
  {Microsporidiiim 
  bombycis) 
  w^as 
  responsible. 
  

   According 
  to 
  Knoch, 
  little 
  refractive 
  granules 
  appear 
  in 
  the 
  blood 
  

   corpuscules 
  ; 
  these 
  multiply 
  and 
  infect 
  the 
  nuclei 
  of 
  tissue 
  cells, 
  where 
  

   their 
  amoeboid 
  membrane 
  hardens 
  and 
  they 
  change 
  into 
  polyhedral 
  

   bodies 
  ; 
  he 
  further 
  states 
  that 
  the 
  minute 
  granules, 
  which 
  resemble 
  

   the 
  Chlamydozoa 
  of 
  Prowazek, 
  are 
  the 
  vegetative, 
  the 
  polyhedral 
  

   bodies 
  the 
  resting 
  stages 
  of 
  the 
  causative 
  organism. 
  Prowazek 
  was 
  

   able 
  to 
  infect 
  caterpillars 
  with 
  the 
  disease 
  by 
  means 
  of 
  a 
  filtrate 
  of 
  

   emulsified 
  diseased 
  material, 
  which 
  contained 
  neither 
  bacteria 
  nor 
  

   polyhedral 
  bodies 
  ; 
  his 
  experiments, 
  in 
  the 
  author's 
  opinion, 
  are 
  

   suggestive, 
  but 
  not 
  conclusive, 
  as 
  no 
  controls 
  were 
  made, 
  and 
  the 
  blood 
  

   test 
  was 
  the 
  only 
  one 
  used 
  in 
  diagnosing 
  the 
  health 
  of 
  the 
  caterpillars. 
  

  

  Thirty 
  filterable 
  viruses 
  are 
  known 
  to 
  be 
  responsible 
  for 
  diseases 
  in 
  

   man 
  and 
  the 
  lower 
  mammals, 
  but 
  only 
  one 
  has 
  been 
  described 
  in 
  insects, 
  

   viz., 
  that 
  of 
  sacbrood, 
  a 
  bee 
  disease 
  discovered 
  by 
  White 
  in 
  1913. 
  

   [See 
  this 
  Review, 
  Ser. 
  A, 
  i, 
  p. 
  186.] 
  

  

  Coming 
  to 
  the 
  experiments 
  made 
  by 
  the 
  authors, 
  it 
  is 
  first 
  stated 
  

   that 
  the 
  reason 
  why 
  filtrates 
  of 
  diseased 
  material 
  gave 
  negative 
  results 
  

   in 
  1912, 
  was 
  that 
  the 
  emulsion 
  was 
  too 
  concentrated. 
  This 
  year, 
  

   caterpillars 
  which 
  died 
  of 
  the 
  disease 
  were 
  crushed 
  with 
  just 
  enough 
  

   sterile 
  water 
  to 
  facilitate 
  the 
  crushing. 
  This 
  material 
  was 
  then 
  

   strained 
  through 
  cheese-cloth 
  and 
  filtered 
  by 
  means 
  of 
  suction 
  through 
  

   filter 
  paper 
  ; 
  the 
  filtrate 
  was 
  diluted 
  in 
  one 
  case 
  with 
  fifty, 
  in 
  another 
  

   with 
  twenty-five 
  times 
  its 
  volume 
  of 
  water. 
  This 
  was 
  then 
  passed 
  

   through 
  a 
  Berkefeld 
  " 
  Grade 
  N 
  " 
  filter 
  and 
  used 
  for 
  the 
  infection 
  

   experiments. 
  The 
  filtrate 
  was 
  free 
  from 
  bacteria 
  and 
  polyhedral 
  

   bodies. 
  Nothing 
  could 
  be 
  observed 
  except 
  some 
  very 
  minute 
  dancing 
  

   granules, 
  also 
  noticed 
  by 
  Prowazek 
  in 
  his 
  experiments 
  with 
  silkworms. 
  

   A 
  large 
  number 
  of 
  caterpillars 
  were 
  fed 
  with 
  the 
  Berkefeld 
  filtrate, 
  

   smeared 
  on 
  red 
  oak 
  leaves. 
  In 
  one 
  series 
  of 
  experiments 
  50 
  cater- 
  

   pillars 
  were 
  fed 
  with 
  the 
  filtrate, 
  in 
  another 
  40, 
  in 
  a 
  third 
  20. 
  The 
  

   same 
  number 
  was 
  fed 
  with 
  material 
  before 
  it 
  was 
  passed 
  through 
  the 
  

   Berkefeld 
  filter, 
  and 
  a 
  large 
  set 
  of 
  controls, 
  fed 
  with 
  Berkefeld 
  filtrate 
  

   which 
  had 
  been 
  sterilised 
  by 
  autoclaving, 
  accompanied 
  each 
  series. 
  

  

  