554 
Nuttall,-^  using  thu'ty  lice,  was  able  to  transmit,  in  the  first  of  two 
experiments,  T.  leivisi  from  an  infected  to  a  normal  animal.  In  the 
second  e.xperiment,  ten  lice  were  transferred  from  a  wild  to  an  un¬ 
infected  rat  without,  however,  giving  rise  to  an  infection  in  the  latter. 
As  he  was  unable  to  trace  any  development  of  T.  leivisi  in  the  rat 
louse,  he  seriously  doubts  whether  any  such  development  occurs. 
Baldry,-^  on  the  other  hand,  working  in  Hartmann’s  laboratory  was 
not  only  able  to  obtain  positive  results  in  his  transmission  experiments, 
but  also  fully  confirms  Prowazek’s  observations  regarding  conjuga¬ 
tion.  Pie  asserts  that  the  developmental  cycle  takes  place  within 
eight  to  ten  days,  and  that  it  is  a  very  small  Crii  hid  id -like  form  of 
T.  lezvisi  in  the  louse  which  gives  rise  to  the  new  infection. 
TRANSMISSION  EXPERIMENTS 
In  three  of  our  experiments  we  have  been  able  to  transmit 
7".  lezvisi  by  means  of  the  rat  louse.  We  usually  collected  well-fed 
lice  from  a  heavily  infected  rat  and  transferred  them,  after  an  interval 
of  twenty  hours,  to  a  normal  rat.  In  one  experiment,  twenty-four,  and 
in  the  other  two  experiments,  forty,  lice  were  used.  In  the  first  two 
cases  parasites  appeared  in  the  peripheral  blood  after  an  incubation 
period  of  eight  days,  and  in  the  third  after  ten  days.  In  each  case 
the  animal  developed  a  typical  infection. 
In  tw'o  further  experiments  ten  lice  were  used  after  having  been 
kept  for  two  days  in  test  tubes,  but  in  neither  did  an  infection  result, 
although  the  unimids  were  kept  under  observation  for  a  considerable 
period. 
Method.  For  the  study  of  the  parasite  in  the  intermediate  host, 
rat-lice  were  collected  from  an  infected  animal.  The  heads  of  the 
lice  were  snipped  off  with  a  small  pair  of  scissors,  and  the  gut  contents 
teased  out  in  a  small  amount  of  physiological  saline  solution.  PJsually 
a  film  \vas  made  of  the  gut  contents  of  five  to  ten  lice,  and  while  still 
wet  dipped  into  Flemming’s  or  Flermann’s  solution,  or  sublimate- 
acetic-alcohol.  F  lemming’s  solution,  however,  gave  the  best  and  most 
satisfactory  results,  and  parasites  fixed  in  this  W'ay  showed  less 
deformity  than  by  an}/  other  method.  If  sublimate-acetic-alcohol 
was  used,  the  parasites  always  seemed  to  be  somewhat  shrunken. 
1  he  specimens  were  stained  with  Breinl’s  safranine-methylene- 
blue  tannm  orange  method  and  Breinl’s  modification  of  Heidenhain, 
