﻿332 
  ANNUA.L 
  REPORT 
  SMITHSONIAN- 
  INSTITUTION, 
  192 
  9 
  

  

  Size. 
  — 
  Essentially 
  they 
  are 
  very 
  small 
  though 
  just 
  how 
  small 
  it 
  is 
  

   impossible 
  to 
  say. 
  They 
  must 
  be 
  ultimately 
  particulate 
  because 
  all 
  

   matter 
  is 
  so 
  arranged, 
  and 
  from 
  the 
  readiness 
  with 
  which 
  they 
  are 
  

   adsorbed 
  on 
  to 
  appropriate 
  surfaces 
  the 
  particles 
  are 
  presumably 
  much 
  

   larger 
  than 
  the 
  molecules 
  of 
  simple 
  salts. 
  Passage 
  through 
  filters 
  

   with 
  pores 
  of 
  different 
  sizes 
  turns 
  out 
  to 
  be 
  a 
  complicated 
  and 
  dubious 
  

   method 
  of 
  measurement, 
  and 
  the 
  effects 
  of 
  centrifugalization 
  may 
  

   depend 
  more 
  on 
  the 
  specific 
  gravity 
  than 
  the 
  size 
  of 
  the 
  particles. 
  

   They 
  are 
  invisible, 
  and 
  ultramicroscopy 
  shows 
  nothing 
  in 
  the 
  infec- 
  

   tive 
  blood 
  of 
  polyhedral 
  caterpillar 
  disease, 
  at 
  least 
  down 
  to 
  50^/* 
  

   (and 
  probably 
  down 
  to 
  ISjuyu), 
  which 
  qualitatively 
  and 
  quantitatively 
  

   can 
  not 
  be 
  seen 
  in 
  normal 
  blood. 
  Levaditi 
  says 
  (in 
  error 
  according 
  to 
  

   Bedson) 
  that 
  herpes 
  virus 
  goes 
  through 
  membranes 
  which 
  hold 
  back 
  

   complement 
  and 
  tetanus 
  toxin; 
  it 
  is 
  possible 
  to 
  concentrate 
  solu- 
  

   tions 
  of 
  haemoglobin 
  in 
  the 
  centrifuge. 
  Taking 
  one 
  thing 
  with 
  another 
  

   and 
  reckoning 
  that 
  some 
  viruses 
  are 
  doubtless 
  larger 
  than 
  others, 
  an 
  

   average 
  diameter 
  of 
  about 
  25 
  mm 
  (0.025 
  /x) 
  seems 
  a 
  reasonable 
  assump- 
  

   tion, 
  about 
  Ko 
  the 
  diameter 
  of 
  the 
  smallest 
  bacillus, 
  about 
  the 
  same 
  

   size 
  as 
  the 
  colloidal 
  aggregates 
  of 
  dissolved 
  haemoglobin 
  and 
  with 
  

   room 
  for 
  200 
  to 
  400 
  proteid 
  molecules. 
  

  

  Now 
  it 
  is 
  characteristic 
  of 
  all 
  groups 
  of 
  animals 
  and 
  plants 
  that 
  they 
  

   have 
  upper 
  and 
  lower 
  limits 
  of 
  size.^ 
  There 
  is 
  no 
  mammal, 
  fish, 
  

   moUusk, 
  or 
  insect 
  which 
  is 
  not 
  perceptible 
  to 
  the 
  bare 
  eye 
  any 
  more 
  

   than 
  there 
  is 
  any 
  bacillus 
  which 
  can 
  be 
  seen 
  without 
  a 
  magnifying 
  glass. 
  

   It 
  is 
  also 
  in 
  a 
  general 
  way 
  true 
  that 
  there 
  is 
  nothing 
  which 
  has 
  the 
  

   properties 
  which 
  we 
  commonly 
  associate 
  with 
  bacteria 
  which 
  is 
  not 
  

   at 
  some 
  stage 
  in 
  its 
  life 
  visible 
  with 
  the 
  highest 
  powers 
  of 
  the 
  ordinary 
  

   microscope 
  or 
  en 
  masse 
  in 
  culture, 
  though 
  of 
  course, 
  if 
  rules 
  of 
  this 
  

   kind 
  were 
  too 
  absolute, 
  thej^ 
  would 
  imply 
  a 
  more 
  anthropomorphic 
  

   world 
  than 
  most 
  people 
  nowadays 
  are 
  prepared 
  to 
  flatter 
  themselves 
  

   with. 
  

  

  Frank 
  bacteria 
  and 
  protozoa 
  may 
  have 
  minute 
  phases: 
  Leishman 
  

   showed 
  long 
  ago 
  that 
  the 
  spirochaete 
  of 
  African 
  relapsing 
  fever 
  might 
  

   in 
  the 
  tick 
  be 
  invisible 
  and 
  filtrable 
  and 
  we 
  can 
  not 
  reject 
  the 
  evidence 
  

   that 
  even 
  the 
  tubercle 
  bacillus 
  may 
  exist 
  in 
  a 
  similar 
  state. 
  But 
  no 
  

   definite 
  bacillus 
  is 
  known 
  which 
  is 
  much 
  smaller 
  than 
  pneumosintes, 
  

   and 
  it 
  seems 
  likely 
  that 
  at 
  a 
  diameter 
  of 
  something 
  like 
  0.25 
  ju 
  (250 
  nn), 
  

   i. 
  e., 
  somewhere 
  about 
  the 
  limit 
  of 
  direct 
  microscopic 
  vision, 
  there 
  is 
  a 
  

   break 
  in 
  the 
  series 
  which 
  runs 
  continuously 
  downward 
  from 
  the 
  larg- 
  

   est 
  bacilli 
  (which 
  would 
  be 
  visible 
  to 
  the 
  naked 
  eye 
  if 
  they 
  were 
  20 
  

   times 
  as 
  big 
  as 
  they 
  are) 
  just 
  as 
  the 
  series 
  of 
  mammals 
  stops 
  at 
  a 
  weight 
  

   of 
  about 
  5 
  grams 
  and 
  the 
  series 
  of 
  beetles 
  at 
  a 
  length 
  of 
  about 
  0.5 
  mm. 
  

   The 
  largest 
  Bacillus 
  megaterium 
  is 
  some 
  25,000 
  times 
  the 
  bulk 
  of 
  Dial- 
  

  

  » 
  See 
  the 
  table 
  in 
  Animal 
  Biology, 
  by 
  J. 
  B. 
  S. 
  Haldanc 
  and 
  J. 
  Huxley 
  1927 
  276, 
  and 
  Contributions 
  to 
  

   Medical 
  and 
  Biological 
  Research 
  (Osier 
  Memorial), 
  1919, 
  i, 
  226. 
  

  

  