0 
555 
as  clesciibed  in  a  previous  paper. The  comparati\’e  use  of  these  two 
inethods  was  of  great  service.  In  the  former  method,  granules,  whicli 
were  often  present  in  large  numbers,  stained  brilliantly  with 
safranine,  at  times  masking  the  nucleus  and  blepharoplast  and  often 
rendering  the  interpretation  of  cytological  details  difficult.  When, 
on  the  other  hand,  Heidenhain’s  haematoxylin  method  was  used  the 
granules  remained  unstained.  In  this  method,  however,  it  was  more 
difficult  to  obtain  as  perfect  a  differentiation  of  the  details  of  the 
nucleus  as  with  safranine  methylene  blue.  Fresh  examination  was 
also  constantly  practised,  and  sometimes  a  parasite  was  kept  under 
observation  for  as  long  as  twenty-four  hours. 
It  seems  surprising  that  Nuttall  and  his  co-workers  were  unable 
to  observe  developmental  changes  in  rat-lice  taken  from  rats  infected 
with  7 .  leivisi.  Howei'er,  for  nearly  four  months  we  sav-  nothing 
liut  degenerated  trypanosomes  in  our  rat-lice,  so  that  we  nearl\' 
abandoned  further  research.  Ultim^itely,  in  one  case  developmental 
forms  were  found  in  lice  taken  from  an  infected  animal,  and  it  became 
apparent  that  during  the  first  stages  of  infection,  so  long  as  dividing 
and  segmenting  forms  were  present  in  the  blood,  the  trypanosomes 
taken  up  by  the  louse  only  degenerated.  On  the  other  hand,  so  soon 
as  division  forms  no  longer  appeared  in  the  peripheral  blood,  the 
trypanosomes  taken  up  by  the  louse  underwent  marked  changes  in 
those  cases  in  which  the  rat’s  blood  was  literally  swarming  with 
trypanosomes.  If,  however,  there  were  only  comparatively  few 
trypanosomes  in  the  blood  (about  seventy  to  eighty  to  a  microscopic 
field),  hardly  any  changes  were  noticeable  in  the  gut  contents  of  the 
louse. 
Thus,  although  nothing  but  degenerated  trypanosomes  were 
present  in  the  gut  contents  of  lice  taken  from  rats  in  the  early 
stages  of  infection,  nevertheless,  developmental  forms  made  their 
appearance  in  the  later  stages  of  the  disease,  but  only  when  the 
blood  of  the  rat  was  literally  swarming  with  trypanosomes. 
The  close  resemblance  of  the  parasites  in  the  gut  of  the  louse  to 
typical  Herpeiomonas  forms  described  by  Prowazek,  Patton,  etc., 
naturally  suggested  that  we  were  perhaps  dealing  with  a  mixed 
infection  in  the  rat  louse — a  natural  infection  with  Herpeiornonas,  and 
a  secondary  infection  with  T.  leivisi. 
We  made  films,  however,  of  the  gut  contents  of  about  6oo  lice 
