557 
hours  becoming'  permanent.  I  hen  the  movements  of  the  parasites 
quickened,  and  a  separation  into  two  halves,  which  was  only  connected 
l3y  a  thin  protoplasmic  strand,  occurred.  The  parasites  often 
remained  at  this  stage,  no  further  changes  occurring.  In  only  a  few 
instances  was  a  further  development  seen  to  take  place  ;  the  anterior 
part  of  the  parasite  appearing  to  disintegrate,  until,  finally,  only  a 
lound  head  with  a  long  rapidly  moving  flagellum  remained.  In  only 
one  case  w^as  the  flagellum  actually  seen  to  become  detached. 
No  further  development  occurred.  We  have  never  been  able  to 
observe  any  process  which  could  be  satisfactorily  explained  as 
representing  conjugation.  Now  and  again,  parasites  apparently 
consisting  of  two  changed  trypanosomes,  joined  at  one  end,  were 
observed.  Although  these  parasites  were  sometimes  kept  under 
observation  for  tw^enty-four  hours  until  all  movement  had  ceased,  m 
no  instance  did  any  transformation  occur  which  could  be  regarded  as 
conjugation.  Tempting  as  it  is  to  regard  certain  appearances  in 
stained  specimens  as  conjugation  forms,  nothing  but  observation  of 
the  whole  process  in  fresh  specimens  can  be  regarded  as  conclusive. 
Small,  round  forms,  as  described  later  in  stained  specimens,  have 
frequently  been  seen  exhibiting  a  circular  movement. 
STAINED  PREPARATIONS 
Changes  analogous  to  those  which  we  have  just  described  can  be 
seen  in  stained  specimens.  For  the  preparation  of  these,  lice  were 
sometimes  used  which  had  been  taken  from  an  infected  rat  and  kept 
alive  in  a  test  tube  for  as  long  as  seventy-two  hours.  After  this  time 
they  usually  died,  unless  put  back  on  another  animal. 
The  trypanosomes  m  the  gut  of  a  louse  taken  shortly  after  the 
height  of  the  infection  was  reached  usually  showed  quite  characteristic 
changes  in  the  nucleus.  Whereas  in  a  normal  blood  trypanosome 
the  nucleus  only  contained  one  intranuclear  centrosome  (karyosome), 
in  the  majority  of  the  louse  parasites,  this  had  divided,  and  the 
division  products  had  moved  to  opposite  ends  of  the  nucleus  (Figs. 
1-3)- 
At  this  stage  forms  w^ere  found  in  which  the  nucleus  had  undergone 
complete  equal  division,  each  half  containing  an.  intranuclear  centro 
some  surrounded  by  a  light  unstained  area  of  karyolymph. 
