﻿83 
  

  

  ON 
  THREE 
  SPECIES 
  OF 
  XENOPSYLLA 
  OCCURRING 
  ON 
  RATS 
  

  

  IN 
  INDIA. 
  

  

  By 
  the 
  Hon. 
  N. 
  Charles 
  Rothschild, 
  M.A., 
  F.L.S. 
  

  

  As 
  it 
  is 
  now 
  generally 
  admitted 
  that 
  one 
  or 
  more 
  of 
  the 
  species 
  of 
  fleas 
  occurring 
  

   on 
  the 
  common 
  rats, 
  Mus 
  rattus 
  and 
  Mus 
  norvegicus, 
  are 
  concerned 
  in 
  the 
  transmission 
  

   of 
  plague, 
  the 
  study 
  of 
  these 
  fleas 
  has 
  become 
  a 
  matter 
  of 
  the 
  highest 
  importance 
  in 
  

   connexion 
  with 
  the 
  prevention 
  of 
  the 
  disease. 
  The 
  first 
  point 
  that 
  demands 
  

   elucidation 
  at 
  the 
  hands 
  of 
  medical 
  entomologists 
  is 
  the 
  identity 
  of 
  the 
  species 
  that 
  

   is 
  or 
  are 
  responsible. 
  When 
  this 
  point 
  has 
  been 
  satisfactorily 
  determined, 
  attention 
  

   can 
  be 
  directed 
  to 
  the 
  detailed 
  study 
  of 
  the 
  bionomics 
  of 
  the 
  obnoxious 
  species, 
  as 
  a 
  

   preliminary 
  to 
  the 
  adoption 
  of 
  appropriate 
  remedial 
  measures. 
  It 
  will 
  be 
  obvious 
  

   that 
  a 
  sine 
  qua 
  non 
  to 
  a 
  successful 
  attack 
  on 
  the 
  problem 
  is 
  the 
  ability 
  of 
  the 
  

   investigator 
  to 
  discriminate 
  the 
  various 
  species 
  that 
  he 
  is 
  likely 
  to 
  meet 
  in 
  his 
  

   researches, 
  and 
  it 
  is 
  the 
  object 
  of 
  the 
  author 
  of 
  these 
  notes 
  to 
  supply 
  a 
  key 
  to 
  the 
  

   identification 
  of 
  the 
  species 
  of 
  Xenopsylla 
  that 
  occur 
  on 
  rats 
  in 
  India. 
  

  

  So 
  far 
  as 
  is 
  known, 
  three 
  species 
  of 
  the 
  genus 
  just 
  named 
  are 
  to 
  be 
  found 
  on 
  Indian 
  

   rats. 
  These 
  species 
  occur 
  in 
  widely 
  varying 
  proportions, 
  according 
  to 
  the 
  part 
  of 
  

   the 
  country 
  in 
  which 
  the 
  hosts 
  are 
  taken. 
  Not 
  infrequently 
  two 
  — 
  and 
  at 
  times 
  all 
  

   the 
  three 
  — 
  species 
  are 
  to 
  be 
  found 
  on 
  a 
  single 
  rat. 
  As 
  it 
  happens, 
  the 
  three 
  species 
  

   are 
  very 
  much 
  alike 
  and 
  can 
  only 
  be 
  distinguished 
  with 
  certainty 
  under 
  a 
  good 
  

   microscope 
  ; 
  a 
  hand-lens 
  is 
  absolutely 
  useless 
  for 
  the 
  purpose. 
  Apart 
  from 
  this, 
  the 
  

   accurate 
  diagnosis 
  of 
  these 
  species 
  requires 
  practice, 
  and 
  it 
  is 
  within 
  the 
  knowledge 
  

   of 
  the 
  author 
  that 
  some 
  medical 
  officers 
  find 
  no 
  little 
  difficulty 
  in 
  connexion 
  with 
  

   this 
  matter. 
  Just 
  as 
  an 
  inflammation 
  of 
  the 
  epidermis 
  does 
  not 
  necessarily 
  denote 
  

   a 
  case 
  of 
  scarlet 
  fever, 
  so 
  the 
  absence 
  of 
  a 
  comb 
  on 
  a 
  rat 
  flea 
  does 
  not 
  prove 
  the 
  species 
  

   to 
  be 
  Xenopsytta 
  cheopis. 
  

  

  Before 
  proceeding 
  to 
  a 
  description 
  of 
  the 
  chief 
  distinguishing 
  characters 
  of 
  the 
  species 
  

   under 
  consideration 
  a 
  few 
  remarks 
  as 
  to 
  the 
  technique 
  of 
  the 
  necessary 
  examination 
  

   may 
  not 
  be 
  amiss. 
  Fleas 
  that 
  have 
  been 
  freshly 
  caught 
  or 
  have 
  been 
  preserved 
  in 
  

   alcohol 
  are 
  sometimes 
  too 
  opaque 
  when 
  examined 
  with 
  a 
  microscope 
  by 
  transmitted 
  

   light. 
  Such 
  specimens 
  must 
  therefore 
  first 
  be 
  cleared. 
  This 
  is 
  best 
  effected 
  by 
  boiling 
  

   them 
  for 
  an 
  hour 
  or 
  more 
  in 
  oil 
  of 
  cloves, 
  after 
  which 
  they 
  should 
  be 
  allowed 
  to 
  

   remain 
  in 
  the 
  oil 
  for 
  a 
  whole 
  day. 
  This 
  procedure 
  however 
  is 
  usually 
  unnecessary, 
  

   as 
  a 
  sufnc*ently 
  clear 
  view 
  can 
  generally 
  be 
  obtained 
  if 
  a 
  moderate 
  pressure 
  is 
  applied 
  

   to 
  the 
  cover-slip 
  under 
  which 
  the 
  specimen 
  is 
  being 
  examined. 
  If 
  the 
  specimen 
  be 
  

   a 
  female 
  and 
  there 
  be 
  a 
  difficulty 
  in 
  observing 
  the 
  receptaculum 
  seminis, 
  it 
  is 
  usually 
  

   possible 
  to 
  carry 
  out 
  the 
  necessary 
  observations 
  by 
  turning 
  the 
  insect 
  over 
  and 
  

   examining 
  it 
  again. 
  It 
  may 
  be 
  added 
  that, 
  although 
  as 
  a 
  general 
  rule 
  most 
  fleas 
  are 
  

   more 
  readily 
  determined 
  from 
  the 
  male 
  sex, 
  in 
  the 
  case 
  of 
  these 
  Xenopsyllas 
  the 
  

   shape 
  of 
  the 
  receptaculum 
  seminis 
  is 
  so 
  distinctive 
  a 
  character 
  that 
  the 
  females 
  are 
  

   probably 
  the 
  easier 
  of 
  the 
  two 
  to 
  identify. 
  

  

  (CIO) 
  F 
  2 
  

  

  